Imaging device and camera system, and driving method of imaging device

ABSTRACT

An imaging device including: a photoelectric converter including first and second electrodes and a conversion layer therebetween; a voltage supplier; an outputter outputting a signal indicating the potential of the second electrode; and a detector detecting the signal level, in which the change rate of the conversion efficiency of the photoelectric converter with respect to a bias voltage, applied between the electrodes, when the bias voltage is in a first range is greater than when the bias voltage is in a second range greater than the first range, and the voltage supplier, when the detected level is less than a first threshold, causes the potential difference between the electrodes to become a first difference, and, when the detected level is greater than or equal to a second threshold greater than or equal to the first threshold, causes the potential difference to become a second difference greater than the first difference.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging device and a camera system.The present disclosure also relates to a driving method of an imagingdevice.

2. Description of the Related Art

In the field of imaging devices, a configuration is known in which,instead of a photodiode, a photoelectric conversion layer is arrangedabove a semiconductor substrate on which a read circuit is formed. Thiskind of configuration is referred to as a stacked type. For example,Japanese Unexamined Patent Application Publication No. 2011-228648discloses an imaging element that has an organic photoelectricconversion layer sandwiched between a pixel electrode and a transparentopposite electrode, above a substrate on which a read circuit is formed.During operation, a predetermined voltage is applied to the oppositeelectrode.

The specification of U.S. Pat. No. 9,054,246 discloses an imaging systemhaving a quantum dot layer that serves as a photoelectric conversionlayer. Furthermore, the specification of U.S. Pat. No. 9,054,246discloses that the gain of the quantum dot layer is adjusted by alteringa potential difference applied between a transparent electrode and apixel electrode arranged on either side of the quantum dot layer.

SUMMARY

In the field of imaging devices, an expansion in dynamic range isrequired.

A non-limiting exemplary embodiment of the present disclosure providesthe following, for example.

In one general aspect, the techniques disclosed here feature an imagingdevice provided with: a photoelectric converter that includes a firstelectrode, a second electrode, and a photoelectric conversion layerlocated between the first electrode and the second electrode; a voltagesupply circuit; an output circuit that is coupled to the secondelectrode, the output circuit being configured to output a signal thatcorresponds to a potential of the second electrode; and a detectioncircuit that is configured to detect a level of the signal from theoutput circuit, wherein the photoelectric converter has photoelectricconversion characteristics in which a first rate of change is greaterthan a second rate of change, the first rate of change being a rate ofchange of a photoelectric conversion efficiency of the photoelectricconverter with respect to a bias voltage applied between the firstelectrode and the second electrode when the bias voltage is in a firstvoltage range, the second rate being a rate of change of thephotoelectric conversion efficiency of the photoelectric converter withrespect to the bias voltage when the bias voltage is in a second voltagerange that is greater than the first voltage range, and the voltagesupply circuit: supplies a voltage to one of the first electrode and thesecond electrode to cause a potential difference between the firstelectrode and the second electrode to be a first potential difference,in a case where the level detected by the detection circuit is less thana first threshold value; and supplies a voltage to the one of the firstelectrode and the second electrode to cause the potential differencebetween the first electrode and the second electrode to be a secondpotential difference that is greater than the first potentialdifference, in a case where the level detected by the detection circuitis greater than or equal to a second threshold value that is greaterthan or equal to the first threshold value.

General or specific aspects may be realized by means of an element, adevice, a system, an integrated circuit, a method, or a computerprogram. Furthermore, general or specific aspects may be realized bymeans of an arbitrary combination of an element, a device, an apparatus,a system, an integrated circuit, a method, and a computer program.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and the drawings. The benefits and/oradvantages may be individually provided by the various embodiments orfeatures disclosed in the specification and the drawings, and need notall be provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically depicting an exemplary configurationof an imaging device according to a first embodiment of the presentdisclosure;

FIG. 2 is a drawing depicting an exemplary circuit configuration of theimaging device depicted in FIG. 1;

FIG. 3A is a cross-sectional view schematically depicting an exemplarydevice structure of a pixel;

FIG. 3B is a schematic cross-sectional view for describing an operationof the pixel in a case where electrons are used as signal charges;

FIG. 4 is a drawing depicting a typical example of the photoelectricconversion characteristics of a photoelectric conversion layer;

FIG. 5 is a drawing for describing an example of a method of determiningspecific ranges for a first voltage range and a second voltage range;

FIG. 6 is a drawing for describing another example of a method ofdetermining specific ranges for the first voltage range and the secondvoltage range;

FIG. 7 is a drawing for describing yet another example of a method ofdetermining specific ranges for the first voltage range and the secondvoltage range;

FIG. 8 is a schematic flowchart depicting a first exemplary operation ofthe imaging device;

FIG. 9 is a schematic cross-sectional view for describing an operationof the pixel when a voltage of 6 V is applied as a first voltage to anopposite electrode;

FIG. 10 is a schematic cross-sectional view for describing an operationof the pixel when a voltage of 6 V is applied as the first voltage tothe opposite electrode, and schematically depicts a state in whichelectron holes are accumulated in an impurity region;

FIG. 11 is a drawing schematically depicting a state in which apotential difference is increased by applying a second voltage to avoltage line from a voltage supply circuit;

FIG. 12 is a drawing schematically depicting a typical example of achange in the level of a signal from an output circuit, with respect toa change in the quantity of light incident on a photoelectric converter,when the first voltage is applied to the opposite electrode, and when asecond voltage is applied to the opposite electrode;

FIG. 13 is a drawing depicting once again the typical example of thephotoelectric conversion characteristics depicted in FIG. 4;

FIG. 14 is a schematic cross-sectional view depicting a configuration inwhich a third electrode is arranged between two pixel electrodes thatare adjacent to each other;

FIG. 15 is a schematic plan view depicting an example of the arrangementrelationship between a pixel electrode and the third electrode, whenseen from the opposite electrode side;

FIG. 16 is a schematic cross-sectional view for describing a mechanismthat lowers the effective photoelectric conversion efficiency byapplying a predetermined voltage to the third electrode;

FIG. 17 is a schematic drawing for describing the relationship between achange in the potential of a node that accompanies the accumulation ofsignal charges, and a power source voltage;

FIG. 18 is a schematic drawing for describing the relationship between achange in the potential of the node that accompanies the accumulation ofsignal charges, and the power source voltage;

FIG. 19 is a drawing depicting a modified example of an output circuitincluded in the pixel;

FIG. 20 is a potential diagram for describing an operation of the outputcircuit depicted in FIG. 19;

FIG. 21 is a drawing depicting a second modified example of the outputcircuit included in the pixel;

FIG. 22 is a drawing depicting a third modified example of the outputcircuit included in the pixel;

FIG. 23 is a drawing depicting a fourth modified example of the outputcircuit included in the pixel;

FIG. 24 is a drawing depicting a specific example of an attenuatordepicted in FIG. 23;

FIG. 25 is a drawing depicting an exemplary circuit configuration of animaging device according to a modified example of the first embodiment;

FIG. 26 is a drawing depicting an exemplary circuit configuration of animaging device according to another modified example of the firstembodiment;

FIG. 27 is a drawing schematically depicting an exemplary configurationof a camera system according to a second embodiment of the presentdisclosure;

FIG. 28 is a drawing schematically depicting another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 29 is a drawing schematically depicting yet another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 30 is a drawing depicting a modified example of a light quantitydetector;

FIG. 31 is a drawing schematically depicting yet another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 32 is a drawing for describing the relationship between the timingof switching between the first voltage and the second voltage, and achange in the level of a signal acquired by a detection circuit, whichaccompanies the switching of the voltage;

FIG. 33 is a drawing depicting another example of the timing ofswitching between the first voltage and the second voltage;

FIG. 34 is a drawing depicting yet another example of the timing ofswitching between the first voltage and the second voltage;

FIG. 35 is a drawing for describing the relationship between the timingof switching between the first voltage and the second voltage when aglobal shutter implemented by controlling a potential difference isapplied, and a change in the level of the signal acquired by thedetection circuit, which accompanies the switching of the voltage;

FIG. 36 is a drawing for describing an example of the relationshipbetween the timing of switching between the first voltage and the secondvoltage, and an output from the imaging device;

FIG. 37 is a drawing depicting an application example of mask processingin a case where switching between the first voltage and the secondvoltage has been executed during a row scanning period for readingsignals;

FIG. 38 is a drawing for describing an example of a processing sequencein an automatic exposure setting process, which can be applied in animaging device and a camera system according to embodiments of thepresent disclosure;

FIG. 39 is a schematic plan view for describing an example in which aregion including the photoelectric converters of some or all of thepixels included in an imaging region is used as an exposure quantitydetection region;

FIG. 40 is a diagram depicting an example of processing in which avoltage that is output from the voltage supply circuit is alteredaccording to the exposure quantity detected;

FIG. 41 is a diagram depicting another example of processing in whichthe voltage that is output from the voltage supply circuit is alteredaccording to the exposure quantity detected;

FIG. 42 is a diagram depicting yet another example of processing inwhich the voltage that is output from the voltage supply circuit isaltered according to the exposure quantity detected;

FIG. 43 is a drawing schematically depicting an example of a change inthe output of the detection circuit, with respect to an increase in theexposure quantity;

FIG. 44 is a block diagram schematically depicting an overview oflinearity compensation processing;

FIG. 45 is a drawing depicting an example of a correction table;

FIG. 46 is a drawing for describing differences in deviation inlinearity according to the imaging device or according to the camerasystem;

FIG. 47 is a block diagram schematically depicting an overview oflinearity compensation processing in which differences according to theimaging device or according to the camera system are canceled;

FIG. 48 is a drawing depicting an example of a correction table storedin a memory of an imaging device of sample 1;

FIG. 49 is a drawing depicting an example of a correction table storedin the memory of an imaging device of sample 2;

FIG. 50 is a drawing depicting another example of a correction tablestored in the memory;

FIG. 51 is a drawing depicting the plotting of output values given inthe correction table of FIG. 50; and

FIG. 52 is a drawing schematically depicting an overview of linearitycompensation processing including interpolation processing.

DETAILED DESCRIPTION

An overview of an aspect of the present disclosure is as follows.

[Item 1]

An imaging device provided with:

a photoelectric converter that includes a first electrode, a secondelectrode, and a photoelectric conversion layer located between thefirst electrode and the second electrode;

a voltage supply circuit;

an output circuit that is coupled to the second electrode, the outputcircuit being configured to output a signal that corresponds to apotential of the second electrode; and

a detection circuit that is configured to detect a level of the signalfrom the output circuit, wherein

the photoelectric converter has photoelectric conversion characteristicsin which a first rate of change is greater than a second rate of change,the first rate of change being a rate of change of a photoelectricconversion efficiency of the photoelectric converter with respect to abias voltage applied between the first electrode and the secondelectrode when the bias voltage is in a first voltage range, the secondrate being a rate of change of the photoelectric conversion efficiencyof the photoelectric converter with respect to the bias voltage when thebias voltage is in a second voltage range that is greater than the firstvoltage range, and

the voltage supply circuit:

-   -   supplies a voltage to one of the first electrode and the second        electrode to cause a potential difference between the first        electrode and the second electrode to be a first potential        difference, in a case where the level detected by the detection        circuit is less than a first threshold value; and    -   supplies a voltage to the one of the first electrode and the        second electrode to cause the potential difference between the        first electrode and the second electrode to be a second        potential difference that is greater than the first potential        difference, in a case where the level detected by the detection        circuit is greater than or equal to a second threshold value        that is greater than or equal to the first threshold value.        [Item 2]

The imaging device according to item 1, wherein

the voltage supply circuit:

-   -   supplies a first voltage to the one of the first electrode and        the second electrode, in a case where the level detected by the        detection circuit is less than the first threshold value; and,    -   supplies a second voltage that is greater than the first voltage        to the one of the first electrode and the second electrode, in a        case where the level detected by the detection circuit is        greater than or equal to the second threshold value.        [Item 3]

The imaging device according to item 2, wherein

the output circuit includes:

-   -   a first transistor that has a gate coupled to the second        electrode, the first transistor being configured to receive a        third voltage to one of a source and a drain; and    -   a second transistor that has a gate coupled to the second        electrode, the second transistor being configured to receive a        fourth voltage that is greater than the third voltage to one of        a source and a drain.        [Item 4]

The imaging device according to item 2, wherein

the output circuit includes:

-   -   a capacitor; and    -   a switching element that is coupled between the second electrode        and the capacitor, and,

the switching element is set to on-state when the signal thatcorresponds to the potential of the second electrode is read, in a casewhere the level detected by the detection circuit is greater than orequal to the second threshold value, the potential of the secondelectrode having been changed by photoelectric conversion in thephotoelectric converter.

[Item 5]

The imaging device according to item 2, wherein

the output circuit includes a capacitor that has one electrode coupledto the second electrode, and,

a potential of another electrode of the capacitor is temporarilydecreased when the signal that corresponds to the potential of thesecond electrode is read, in a case where the level detected by thedetection circuit is greater than or equal to the second thresholdvalue, the potential of the second electrode having been changed byphotoelectric conversion in the photoelectric converter.

[Item 6]

The imaging device according to item 2, wherein

the output circuit includes:

-   -   a first transistor that has a gate coupled to the second        electrode; and    -   an attenuator that is coupled between the second electrode and        the gate of the first transistor, and,

the attenuator attenuates a voltage applied to the gate of the firsttransistor, in a case where the level detected by the detection circuitis greater than or equal to the second threshold value.

[Item 7]

The imaging device according to any one of items 2 to 6, wherein apotential of the first electrode is greater than the potential of thesecond electrode, in both of a state in which the first voltage issupplied to the one of the first electrode and the second electrode, anda state in which the second voltage is supplied to the one of the firstelectrode and the second electrode.

[Item 8]

The imaging device according to any one of items 2 to 7, wherein, in agraph of the photoelectric conversion efficiency of the photoelectricconverter with respect to the bias voltage, when Vt is a value of thebias voltage corresponding to an intersecting point between a firsttangent at a point where the photoelectric conversion efficiency risesfrom 0 and a second tangent at a point where the bias voltage is alargest value during operation, the first voltage range is a voltagerange that is less than the Vt.

[Item 9]

The imaging device according to any one of items 2 to 7, wherein, in agraph of the photoelectric conversion efficiency of the photoelectricconverter with respect to the bias voltage, when Vt is a value of thebias voltage corresponding to an intersecting point between a firsttangent at a point where a value of the photoelectric conversionefficiency is 0.06 and a second tangent at a point where the biasvoltage is a largest value during operation, the first voltage range isa voltage range that is less than the Vt.

[Item 10]

The imaging device according to any one of items 2 to 7, wherein thesecond voltage range is a voltage range in which a change in thephotoelectric conversion efficiency with respect to a change of 1 V inthe bias voltage is less than 10%.

[Item 11]

The imaging device according to any one of items 2 to 7, wherein thesecond voltage range is a voltage range in which the photoelectricconversion efficiency is 0.7 or more.

[Item 12]

The imaging device according to any one of items 8 to 11, wherein afirst efficiency that is the photoelectric conversion efficiency of thephotoelectric converter when the first voltage is supplied is less thana second efficiency that is the photoelectric conversion efficiency ofthe photoelectric converter when the second voltage is supplied.

[Item 13]

The imaging device according to item 12, wherein the first voltage andthe second voltage are voltages within the second voltage range.

[Item 14]

The imaging device according to item 13, wherein a ratio of the secondefficiency with respect to the first efficiency is greater than 1 and1.25 or less.

[Item 15]

A camera system provided with:

an imaging device that includes:

-   -   a photoelectric converter that includes a first electrode, a        second electrode, and a photoelectric conversion layer located        between the first electrode and the second electrode;    -   a voltage supply circuit; and    -   an output circuit that is coupled to the second electrode, the        output circuit being configured to output a signal that        corresponds to a potential of the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric converter, wherein

the photoelectric converter has photoelectric conversion characteristicsin which a first rate of change is greater than a second rate of change,the first rate of change being a rate of change of a photoelectricconversion efficiency of the photoelectric converter with respect to abias voltage applied between the first electrode and the secondelectrode when the bias voltage is in a first voltage range, the secondrate being a rate of change of the photoelectric conversion efficiencyof the photoelectric converter with respect to the bias voltage when thebias voltage is in a second voltage range that is greater than the firstvoltage range, and

the voltage supply circuit:

-   -   supplies a voltage to one of the first electrode and the second        electrode to cause a potential difference between the first        electrode and the second electrode to be a first potential        difference, in a case where the quantity of light detected by        the light quantity detector is less than a first quantity of        light; and,    -   supplies a voltage to the one of the first electrode and the        second electrode to cause the potential difference between the        first electrode and the second electrode to be a second        potential difference that is greater than the first potential        difference, in a case where the quantity of light detected by        the light quantity detector is greater than or equal to a second        quantity of light that is greater than or equal to the first        quantity of light.        [Item 16]

A driving method of an imaging device that has a photoelectric converterthat includes a first electrode, a second electrode, and a photoelectricconversion layer located between the first electrode and the secondelectrode, the driving method comprising:

supplying a voltage to one of the first electrode and the secondelectrode to cause a potential difference between the first electrodeand the second electrode to be a first potential difference, in a casewhere a quantity of light incident on the photoelectric converter isless than a first quantity of light; and

supplying a voltage to the one of the first electrode and the secondelectrode to cause the potential difference between the first electrodeand the second electrode to be a second potential difference that isgreater than the first potential difference, in a case where thequantity of light incident on the photoelectric converter is greaterthan or equal to a second quantity of light that is greater than orequal to the first quantity of light.

[Item 17]

An imaging device provided with:

a photoelectric converter that includes a first electrode, a secondelectrode, and a photoelectric conversion layer located between thefirst electrode and the second electrode;

a voltage supply circuit that is electrically coupled to one of thefirst electrode and the second electrode;

an output circuit that is electrically coupled to the second electrodeand outputs a signal that corresponds to a potential of the secondelectrode; and

a detection circuit that detects a level of the signal from the outputcircuit,

in which a rate of change of a photoelectric conversion efficiency ofthe photoelectric converter with respect to a bias voltage, which isapplied between the first electrode and the second electrode, when thebias voltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the level detected by the detection circuit is lowerthan a predetermined threshold value, applies a voltage to the one ofthe first electrode and the second electrode in such a way that apotential difference between the first electrode and the secondelectrode becomes a first potential difference, and,

in a case where the level detected by the detection circuit is greaterthan or equal to the threshold value, applies a voltage to the one ofthe first electrode and the second electrode in such a way that thepotential difference between the first electrode and the secondelectrode becomes a second potential difference that is greater than thefirst potential difference.

According to the configuration of item 17, in a situation where theilluminance is high, the bias voltage that is applied between the firstelectrode and the second electrode increases, and therefore thephotoelectric converter can be driven in a voltage region in which therate of change in the photoelectric conversion efficiency with respectto the bias voltage is relatively small. As a result, it becomespossible to ensure linearity in a wider range, and the dynamic range canbe expanded by means of electrical control. Furthermore, in a situationwhere the illuminance is low, the bias voltage applied between the firstelectrode and the second electrode can be made to be relatively low, andtherefore the effect of suppressing power consumption can be expected.

[Item 18]

The imaging device according to item 17,

in which the voltage supply circuit,

in a case where the level detected by the detection circuit is lowerthan the threshold value, applies a first voltage to the one of thefirst electrode and the second electrode, and, in a case where the leveldetected by the detection circuit is greater than or equal to thethreshold value, applies a second voltage that is higher than the firstvoltage to the one of the first electrode and the second electrode.

According to the configuration of item 18, in a situation where theilluminance is high, from among the mutually different voltages, therelatively high second voltage is selectively applied to thephotoelectric converter from the voltage supply circuit. It thereforebecomes possible to reduce power consumption.

[Item 19]

The imaging device according to item 18,

in which the output circuit includes:

a first signal detection transistor that has a gate electrically coupledto the second electrode, and receives a third voltage to one of a drainand a source; and

a second signal detection transistor that has a gate electricallycoupled to the second electrode, and receives a fourth voltage that ishigher than the third voltage to one of a drain and a source.

According to the configuration of item 19, a capacitor is coupled to thesecond electrode by way of a reset transistor when a signal is read, andtherefore the level of input to a source follower, for example, can betemporarily reduced to a level that is less than a power source voltage.Therefore, even in a case such as where the potential of the secondelectrode exceeds the power source voltage, for example, it becomespossible to read a signal by means of a source follower without boostingthe power source voltage.

[Item 20]

The imaging device according to item 18,

in which the output circuit includes:

a capacitor; and

a switching element that is coupled between the second electrode and thecapacitor, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, the switching element is set toon-state when the signal that corresponds to the potential of the secondelectrode and has been changed by photoelectric conversion in thephotoelectric converter is read.

According to the configuration of item 20, whether or not signal readingis to be carried out can be switched by way of either of two sourcefollowers having mutually different magnitudes for source follower powersources, in accordance with the potential of the second electrode. Ittherefore becomes possible to read a signal even in a case such as wherethe potential of the second electrode exceeds the power source voltage,for example.

[Item 21]

The imaging device according to item 18,

in which the output circuit includes a capacitor that has one electrodecoupled to the second electrode, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, a potential of another electrode ofthe capacitor is temporarily decreased when the signal that correspondsto the potential of the second electrode and has been changed byphotoelectric conversion in the photoelectric converter is read.

According to the configuration of item 21, even in a case such as wherethe potential of the second electrode exceeds the power source voltage,the potential of the second electrode can be selectively lowered when asignal is read. Therefore, even in a case such as where the potential ofthe second electrode exceeds the power source voltage, for example, itbecomes possible to read a signal by means of a source follower withoutboosting the power source voltage.

[Item 22]

The imaging device according to item 18,

in which the output circuit includes:

a first signal detection transistor that has a gate electrically coupledto the second electrode; and

an attenuator that is coupled between the second electrode and the gateof the first signal detection transistor, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, the attenuator attenuates a voltageapplied to the gate of the first signal detection transistor, by apredetermined proportion.

According to the configuration of item 22, even in a case such as wherethe potential of the second electrode exceeds the power source voltage,the level of input to a source follower, for example, can be attenuatedby a predetermined proportion. Therefore, even in a case such as wherethe potential of the second electrode exceeds the power source voltage,for example, it becomes possible to read a signal by means of a sourcefollower without boosting the power source voltage.

[Item 23]

The imaging device according to any one of items 18 to 22,

in which a potential of the first electrode is higher than the potentialof the second electrode in both of a state in which the first voltage isapplied to the one of the first electrode and the second electrode and astate in which the second voltage is applied to the one of the firstelectrode and the second electrode.

According to the configuration of item 23, positive charges from amongthe charges generated by photoelectric conversion can be collected bythe second electrode, and electron holes can be accumulated in a chargeaccumulation region as signal charges. Furthermore, the potential of thecharge accumulation region gradually rises due to continued accumulationof the signal charges, and therefore the effective bias voltageaccording to the photoelectric conversion layer can be made to be lessthan the value of the second voltage.

[Item 24]

The imaging device according to any one of items 18 to 23, in which,

in a graph of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage, when Vt is avalue of the bias voltage corresponding to an intersecting point betweena first tangent at a point where the photoelectric conversion efficiencyrises from 0 and a second tangent at a point where the bias voltage isthe largest value during operation, the first voltage range is a voltagerange that is less than Vt.

[Item 25]

The imaging device according to any one of items 18 to 23, in which,

in a graph of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage, when Vt is avalue of the bias voltage corresponding to an intersecting point betweena first tangent at a point where the value of the photoelectricconversion efficiency becomes 0.06 and a second tangent at a point wherethe bias voltage is the largest value during operation, the firstvoltage range is a voltage range that is less than Vt.

[Item 26]

The imaging device according to any one of items 18 to 23,

in which the second voltage range is a voltage range in which a changein the photoelectric conversion efficiency with respect to a change of 1V in the bias voltage is less than 10%.

[Item 27]

The imaging device according to any one of items 18 to 23,

in which the second voltage range is a voltage range in which thephotoelectric conversion efficiency is 0.7 or more.

According to the configuration of item 27, it is easy to achievecorrespondence between the magnitude of the bias voltage applied betweenthe first electrode and the second electrode and ISO numerical values.

[Item 28]

The imaging device according to any one of items 24 to 27,

in which a first efficiency that is the photoelectric conversionefficiency of the photoelectric converter when the first voltage isbeing supplied is lower than a second efficiency that is thephotoelectric conversion efficiency of the photoelectric converter whenthe second voltage is being supplied.

[Item 29]

The imaging device according to item 28,

in which the first voltage and the second voltage are voltages withinthe second voltage range.

According to the configuration of item 29, an advantage can be obtainedin that reliability is easily ensured since high-voltage elements arenot required, and power saving and high-speed driving can be expectedwhen the first voltage is being supplied.

[Item 30]

The imaging device according to item 29,

in which the ratio of the second efficiency with respect to the firstefficiency is 1 or more and 1.25 or less.

[Item 31]

The imaging device according to any one of items 17 to 30,

further provided with a charge accumulation unit that is electricallycoupled to the second electrode and temporarily accumulates chargescollected by the second electrode,

in which a potential of the charge accumulation unit increases togetherwith accumulation of charges in the charge accumulation unit.

According to the configuration of item 31, high-voltage elements andelement isolation regions are not required, and therefore reliability iseasily ensured.

[Item 32]

The imaging device according to any one of items 17 to 31,

including a plurality of pixels each having a photoelectric converterand an output circuit,

the plurality of pixels including a first pixel and a second pixel thatis arranged adjacent to the first pixel, and

further provided with a third electrode that is located between thesecond electrode of the first pixel and the second electrode of thesecond pixel, and is electrically insulated from the second electrode ofthe first pixel and the second electrode of the second pixel.

According to the configuration of item 32, by adjusting the potential ofthe third electrode, it is possible for charges generated in thevicinity of the boundary between the two pixels to be preferentiallycollected by the third electrode. As a result, it becomes possible forthe effective photoelectric conversion efficiency to be furtherdecreased, and the dynamic range relating to the direction in which theilluminance is high to be further expanded.

[Item 33]

A camera system provided with:

an imaging device that has a photoelectric converter that includes afirst electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode; and

a voltage supply circuit that is electrically coupled to one of thefirst electrode and the second electrode,

in which the imaging device further has:

an output circuit that is electrically coupled to the second electrodeand outputs a signal that corresponds to a potential of the secondelectrode; and

a detection circuit that detects a level of the signal from the outputcircuit,

a rate of change of a photoelectric conversion efficiency of thephotoelectric converter with respect to a bias voltage, which is appliedbetween the first electrode and the second electrode, when the biasvoltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the level detected by the detection circuit is lowerthan a predetermined threshold value, applies a voltage to the one ofthe first electrode and the second electrode in such a way that apotential difference between the first electrode and the secondelectrode becomes a first potential difference, and,

in a case where the level detected by the detection circuit is greaterthan or equal to the threshold value, applies a voltage to the one ofthe first electrode and the second electrode in such a way that thepotential difference between the first electrode and the secondelectrode becomes a second potential difference that is greater than thefirst potential difference.

According to the configuration of item 33, an effect that is similar tothat of item 17 can be obtained.

[Item 34]

The camera system according to item 33,

in which the voltage supply circuit,

in a case where the level detected by the detection circuit is lowerthan the threshold value, applies a first voltage to the one of thefirst electrode and the second electrode, and,

in a case where the level detected by the detection circuit is greaterthan or equal to the threshold value, applies a second voltage that ishigher than the first voltage to the one of the first electrode and thesecond electrode.

According to the configuration of item 34, an effect that is similar tothat of item 18 can be obtained.

[Item 35]

The camera system according to item 34,

in which the output circuit includes:

a capacitor; and

a switching element that is coupled between the second electrode and thecapacitor, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, the switching element is set toon-state when the signal that corresponds to the potential of the secondelectrode and has been changed by photoelectric conversion in thephotoelectric converter is read.

According to the configuration of item 35, an effect that is similar tothat of item 20 can be obtained.

[Item 36]

The camera system according to item 34,

in which the output circuit includes a capacitor that has one electrodecoupled to the second electrode, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, a potential of another electrode ofthe capacitor is temporarily decreased when the signal that correspondsto the potential of the second electrode and has been changed byphotoelectric conversion in the photoelectric converter is read.

According to the configuration of item 36, an effect that is similar tothat of item 21 can be obtained.

[Item 37]

The camera system according to item 34,

in which the output circuit includes:

a first signal detection transistor that has a gate electrically coupledto the second electrode; and

an attenuator that is coupled between the second electrode and the gateof the first signal detection transistor, and,

in a case where the level detected by the detection circuit is greaterthan or equal to a threshold value, the attenuator attenuates a voltageapplied to the gate of the first signal detection transistor, by apredetermined proportion.

According to the configuration of item 37, an effect that is similar tothat of item 22 can be obtained.

[Item 38]

A camera system provided with:

an imaging device that has a photoelectric converter that includes afirst electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric converter,

in which the imaging device further has:

an output circuit that is electrically coupled to the second electrodeand outputs a signal that corresponds to a potential of the secondelectrode; and

a voltage supply circuit that is electrically coupled to one of thefirst electrode and the second electrode,

a rate of change of a photoelectric conversion efficiency of thephotoelectric converter with respect to a bias voltage, which is appliedbetween the first electrode and the second electrode, when the biasvoltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is less than a predetermined quantity of light, applies avoltage to the one of the first electrode and the second electrode insuch a way that a potential difference between the first electrode andthe second electrode becomes a first potential difference, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, applies a voltage to the one of the first electrode and thesecond electrode in such a way that the potential difference between thefirst electrode and the second electrode becomes a second potentialdifference that is greater than the first potential difference.

According to the configuration of item 38, an effect that is similar tothat of item 17 can be obtained.

[Item 39]

A camera system provided with:

an imaging device that has a photoelectric converter that includes afirst electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode;

a voltage supply circuit that is electrically coupled to one of thefirst electrode and the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric converter,

in which a rate of change of a photoelectric conversion efficiency ofthe photoelectric converter with respect to a bias voltage, which isapplied between the first electrode and the second electrode, when thebias voltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range,

the imaging device further has an output circuit that is electricallycoupled to the second electrode and outputs a signal that corresponds toa potential of the second electrode, and

the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is less than a predetermined quantity of light, applies avoltage to the one of the first electrode and the second electrode insuch a way that a potential difference between the first electrode andthe second electrode becomes a first potential difference, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, applies a voltage to the one of the first electrode and thesecond electrode in such a way that the potential difference between thefirst electrode and the second electrode becomes a second potentialdifference that is greater than the first potential difference.

According to the configuration of item 39, an effect that is similar tothat of item 17 can be obtained.

[Item 40]

The camera system according to item 38 or 39,

in which the light quantity detector includes a light quantity detectioncircuit that detects the level of the signal from the output circuit.

According to the configuration of item 40, information relating to thequantity of light incident on the photoelectric converter can beobtained by way of detecting the level of the signal that is output froma pixel.

[Item 41]

The camera system according to any one of items 38 to 40,

in which the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is less than the predetermined quantity of light, applies afirst voltage to the one of the first electrode and the secondelectrode, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, applies a second voltage that is higher than the first voltage tothe one of the first electrode and the second electrode.

According to the configuration of item 41, an effect that is similar tothat of item 18 can be obtained.

[Item 42]

The camera system according to item 34 or 41,

in which the output circuit includes:

a first signal detection transistor that has a gate electrically coupledto the second electrode, and receives a third voltage to one of a drainand a source; and

a second signal detection transistor that has a gate electricallycoupled to the second electrode, and receives a fourth voltage that ishigher than the third voltage to one of a drain and a source.

According to the configuration of item 42, an effect that is similar tothat of item 19 can be obtained.

[Item 43]

The camera system according to item 41,

in which the output circuit includes:

a capacitor; and

a switching element that is coupled between the second electrode and thecapacitor, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, the switching element is set to on-state when the signal thatcorresponds to the potential of the second electrode and has beenchanged by photoelectric conversion in the photoelectric converter isread.

According to the configuration of item 43, an effect that is similar tothat of item 20 can be obtained.

[Item 44]

The camera system according to item 41,

in which the output circuit includes a capacitor that has one electrodecoupled to the second electrode, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, a potential of another electrode of the capacitor is temporarilydecreased when the signal that corresponds to the potential of thesecond electrode and has been changed by photoelectric conversion in thephotoelectric converter is read.

According to the configuration of item 44, an effect that is similar tothat of item 21 can be obtained.

[Item 45]

The camera system according to item 41,

in which the output circuit includes:

a first signal detection transistor that has a gate electrically coupledto the second electrode; and

an attenuator that is coupled between the second electrode and the gateof the first signal detection transistor, and,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to a predetermined quantity of light,the attenuator attenuates a voltage applied to the gate of the firstsignal detection transistor, by a predetermined proportion.

According to the configuration of item 45, an effect that is similar tothat of item 22 can be obtained.

[Item 46]

The camera system according to item 34, 35, 36, 37, 41, 42, 43, 44, or45,

in which a potential of the first electrode is higher than the potentialof the second electrode in both of a state in which the first voltage isapplied to the one of the first electrode and the second electrode and astate in which the second voltage is applied to the one of the firstelectrode and the second electrode.

According to the configuration of item 46, an effect that is similar tothat of item 23 can be obtained.

[Item 47]

The camera system according to item 34, 35, 36, 37, 41, 42, 43, 44, 45,or 46,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage, when Vt is avalue of the bias voltage corresponding to an intersecting point betweena first tangent at a point where the photoelectric conversion efficiencyrises from 0 and a second tangent at a point where the bias voltage isthe largest value during operation, the first voltage range is a voltagerange that is less than Vt.

[Item 48]

The camera system according to item 34, 35, 36, 37, 41, 42, 43, 44, 45,or 46,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage, when Vt is avalue of the bias voltage corresponding to an intersecting point betweena first tangent at a point where a value of the photoelectric conversionefficiency becomes 0.06 and a second tangent at a point where the biasvoltage is the largest value during operation, the first voltage rangeis a voltage range that is less than Vt.

[Item 49]

The camera system according to item 34, 35, 36, 37, 41, 42, 43, 44, 45,or 46,

in which the second voltage range is a voltage range in which a changein the photoelectric conversion efficiency with respect to a change of 1V in the bias voltage is less than 10%.

[Item 50]

The camera system according to item 34, 35, 36, 37, 41, 42, 43, 44, 45,or 46,

in which the second voltage range is a voltage range in which thephotoelectric conversion efficiency is 0.7 or more.

According to the configuration of item 50, an effect that is similar tothat of item 27 can be obtained.

[Item 51]

The camera system according to any one of items 47 to 50,

in which a first efficiency that is the photoelectric conversionefficiency of the photoelectric converter when the first voltage isbeing supplied is lower than a second efficiency that is thephotoelectric conversion efficiency of the photoelectric converter whenthe second voltage is being supplied.

[Item 52]

The camera system according to item 51,

in which the first voltage and the second voltage are voltages withinthe second voltage range.

According to the configuration of item 52, an effect that is similar tothat of item 29 can be obtained.

[Item 53]

The camera system according to item 52,

in which the ratio of the second efficiency with respect to the firstefficiency is 1 or more and 1.25 or less.

[Item 54]

The camera system according to any one of items 33 to 53,

further provided with a charge accumulation unit that is electricallycoupled to the second electrode and temporarily accumulates chargescollected by the second electrode,

in which a potential of the charge accumulation unit increases togetherwith accumulation of charges in the charge accumulation unit.

According to the configuration of item 54, an effect that is similar tothat of item 31 can be obtained.

[Item 55]

The camera system according to any one of items 33 to 54,

in which the imaging device includes a plurality of pixels each having aphotoelectric converter and an output circuit,

the plurality of pixels include a first pixel and a second pixel that isarranged adjacent to the first pixel, and

the imaging device is further provided with a third electrode that islocated between the second electrode of the first pixel and the secondelectrode of the second pixel, and is electrically insulated from thesecond electrode of the first pixel and the second electrode of thesecond pixel.

According to the configuration of item 55, an effect that is similar tothat of item 32 can be obtained.

[Item 56]

A driving method of an imaging device that has a photoelectric converterthat includes a first electrode, a second electrode, and a photoelectricconversion layer located between the first electrode and the secondelectrode,

in which, in a case where a quantity of light incident on thephotoelectric converter is less than a predetermined quantity of light,a voltage is applied to one of the first electrode and the secondelectrode in such a way that a potential difference between the firstelectrode and the second electrode becomes a first potential difference,and, in a case where the quantity of light incident on the photoelectricconverter is greater than or equal to the predetermined quantity oflight, a voltage is applied to the one of the first electrode and thesecond electrode in such a way that the potential difference between thefirst electrode and the second electrode becomes a second potentialdifference that is greater than the first potential difference.

According to the configuration of item 56, it is possible to expand thedynamic range relating to the direction in which the illuminance ishigh, by means of electrical control.

[Item 57]

The driving method of an imaging device according to item 56,

in which, in a case where a quantity of light incident on thephotoelectric converter is less than the predetermined quantity oflight, a first voltage is applied to one of the first electrode and thesecond electrode, and, in a case where the quantity of light incident onthe photoelectric converter is greater than or equal to thepredetermined quantity of light, a second voltage that is higher thanthe first voltage is applied to the one of the first electrode and thesecond electrode.

According to the configuration of item 57, an effect that is similar tothat of item 18 can be obtained.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the drawings. It should be noted that theembodiments described hereinafter all represent general or specificexamples. The numerical values, the shapes, the materials, theconstituent elements, the arrangement of the constituent elements, themode of connection, the steps, and the order of the steps and so forthgiven in the following embodiments are examples and are not intended torestrict the present disclosure. The various aspects described in thepresent specification may be combined with each other provided there areno resulting inconsistencies. Furthermore, from among the constituentelements in the following embodiments, constituent elements that are notmentioned in the independent claims indicating the most significantconcepts are described as optional constituent elements. In thefollowing description, constituent elements having substantially thesame functions are denoted by common reference characters, anddescriptions thereof are sometimes omitted. Furthermore, some elementsare sometimes not depicted to avoid the drawings becoming overlycomplicated.

First Embodiment

FIG. 1 schematically depicts a configuration of an imaging deviceaccording to a first embodiment of the present disclosure. An imagingdevice 100A depicted in FIG. 1 has a plurality of pixels Px eachincluding in a portion thereof a photoelectric converter supported on asemiconductor substrate 110. Although not depicted in FIG. 1, thesemiconductor substrate 110 has a plurality of output circuits formedrespectively corresponding to the pixels Px.

The plurality of pixels Px are arranged two-dimensionally, for example,on the semiconductor substrate 110, and thereby form an imaging region.The quantity and arrangement of the pixels Px are not restricted to theexample depicted in FIG. 1 and are arbitrary. For example, by arrangingthe plurality of pixels Px one-dimensionally, the imaging device 100Acan be used as a line sensor.

As described in detail hereinafter with reference to the drawings, thephotoelectric converter of each pixel Px has a pixel electrode, atransparent opposite electrode, and a photoelectric conversion layersandwiched between these electrodes. Typically, a plurality of pixelelectrodes are arranged in the imaging region corresponding to thepixels Px, whereas an opposite electrode is provided in the form of asingle electrode layer that is continuous among the plurality of pixelsPx. That is, typically, the potential of the opposite electrode iscommon among the plurality of pixels Px. Similarly for the photoelectricconversion layer, a continuous single photoelectric conversion structurecan be shared among the plurality of pixels Px. In other words, thephotoelectric converter of each pixel Px includes part of a singletransparent electrode that is continuous among the plurality of pixelsPx and part of a continuous single photoelectric conversion structure.

In the configuration exemplified in FIG. 1, the imaging device 100Aincludes a row scanning circuit 120 that is coupled to each pixel Px viarow signal lines Ri, and a detection circuit 130A that is coupled toeach pixel Px via output signal lines S_(j). Here, the subscript m and nappended to the reference characters in FIG. 1 independently representan integer greater than or equal to 1. The row signal lines R^(i) areprovided for each row of the plurality of pixels Px, and areelectrically coupled to one or more pixels Px belonging to the same row.In FIG. 1, for simplicity, the row signal lines Rare representativelydepicted as signal lines coupled to the row scanning circuit 120;however, it is also possible for two or more signal lines to be providedfor each row of the plurality of pixels Px. The output signal linesS_(j) are provided for each column of the plurality of pixels Px, andare electrically coupled to the output circuit of one or more pixels Pxbelonging to the same row. As depicted, each of the output signal linesS_(j) is coupled to the detection circuit 130A.

Typically, the detection circuit 130A includes in a portion thereof acircuit for carrying out noise-suppression signal processing representedby correlated double sampling, analog-digital conversion, and the like.Pixel signals that express an image of an object are read to outside ofthe imaging device 100A as an output of the detection circuit 130A.

Here, the detection circuit 130A has the function of detecting the levelof output signals that are read from the pixels Px via the output signallines S_(j). In this example, a reference line 132 is coupled to thedetection circuit 130A. Voltage V_(ref) is applied to the reference line132 during operation. The detection circuit 130A may have one or morecomparators 134 that output comparison results of the voltage level ofeach output signal line S_(j), which is the voltage level of each outputsignal line S_(j), and the voltage level of the reference line 132, forexample. The comparison of the voltage levels may be executed in theform of comparing analog values or may be executed in the form ofcomparing digital values.

In the configuration exemplified in FIG. 1, the imaging device 100A alsohas a voltage supply circuit 150 and a control circuit 160. The voltagesupply circuit 150 is coupled to a voltage line 152 that is coupled tothe aforementioned opposite electrode, for example, and is therebycoupled to each pixel Px. The voltage supply circuit 150 supplies apredetermined voltage via the voltage line 152 to the photoelectricconverter of each pixel Px during operation of the imaging device 100A.

The voltage supply circuit 150 is configured so as to be able to atleast switch between and apply two or more different voltages to thevoltage line 152. The voltage that is output from the voltage supplycircuit 150 may be altered in steps or may be altered continuously. Thevoltage supply circuit 150 is not restricted to a specific power sourcecircuit, and may be a circuit that converts a voltage supplied from apower source such as a battery into a predetermined voltage, or may be acircuit that generates a predetermined voltage. The voltage supplycircuit 150 may be part of the row scanning circuit 120.

The control circuit 160 receives command data, a clock, and the likesupplied from outside, for example, for the imaging device 100A andcontrols the entirety of the imaging device 100A. The control circuit160 can be realized by means of a microcontroller including one or moreprocessors, for example. The control circuit 160 can include one or morememories. In the configuration exemplified in FIG. 1, the controlcircuit 160 includes in a portion thereof a memory 162. The memory 162may be provided in the form of a chip or a package separate from theimaging device 100A.

In this example, an image processing circuit 164 is coupled to thecontrol circuit 160. The image processing circuit 164 can be realized bymeans of a digital signal processor (DSP), an image signal processor(ISP), an field-programmable gate array (FPGA), or the like. The imageprocessing circuit 164 may be part of the control circuit 160.

Typically, the control circuit 160 has a timing generator, and suppliesdrive signals to the row scanning circuit 120, the detection circuit130A, the voltage supply circuit 150, and the like. In FIG. 1, the arrowextending to the control circuit 160 and the arrows extending from thecontrol circuit 160 schematically represent an input signal to thecontrol circuit 160 and output signals from the control circuit 160,respectively. Furthermore, in this example, the control circuit 160 isconfigured so as to receive comparison results between the level of theoutput signals from the pixels Px of each column and the voltage levelof the reference line 132 from the detection circuit 130A, and supplydrive signals corresponding to the voltage level comparison results tothe voltage supply circuit 150.

In a case where, for example, the level of the output signals detectedby the detection circuit 130A is lower than the voltage level of thereference line 132, on the basis of a drive signal from the controlcircuit 160, the voltage supply circuit 150 applies a voltage to thevoltage line 152 such that a potential difference applied between theopposite electrode and the pixel electrode of the photoelectricconverters becomes a first potential difference. In a case where thelevel of the output signals detected by the detection circuit 130A isgreater than or equal to the voltage level of the reference line 132, avoltage is applied to the voltage line 152 such that the potentialdifference applied between the opposite electrode and the pixelelectrode becomes a second potential difference that is greater than thefirst potential difference. The voltage supply circuit 150, for example,applies a first voltage V1 to the voltage line 152 in a case where thelevel of the output signals detected by the detection circuit 130A islower than the voltage level of the reference line 132, and applies asecond voltage V2 that is higher than the first voltage V1 in a casewhere the level of the output signals detected by the detection circuit130A is greater than or equal to the voltage level of the reference line132. Typically, in a case where the illuminance on the photoelectricconverters is comparatively high, the level of the output signals fromthe detection circuit 130A is greater than or equal to the voltage levelof the reference line 132. That is, in the present embodiment, thepotential difference applied between the opposite electrode and thepixel electrode of the photoelectric converters is controlled bychanging the voltage applied to the opposite electrode, for example, ofthe photoelectric converters in accordance with the illuminance on thephotoelectric converters.

In a case where the level of the output signals detected by thedetection circuit 130A is lower than the voltage level of the referenceline 132, for example, in a case where the first voltage V1 is appliedto the voltage line 152 and the illuminance on the photoelectricconverters is comparatively high, the relatively high second voltage V2is applied to the voltage line 152. According to this kind of mode, thevoltage applied to the photoelectric converters is increased asrequired, and it is therefore possible to suppress power consumption ina standard photographing mode.

As described in detail hereinafter, the photoelectric converters of thepixels Px can have photoelectric conversion characteristics in which thephotoelectric conversion efficiency increases in accordance with anincrease in a bias voltage between the opposite electrode and the pixelelectrode. Furthermore, the photoelectric converters typically havephotoelectric conversion characteristics with which, when the biasvoltage applied between the pixel electrode and the opposite electrodeis in a second voltage range that is higher than the first voltagerange, the rate of change in the photoelectric conversion efficiencydecreases compared to when the bias voltage is in the first voltagerange. By means of control that increases the bias voltage between theopposite electrode and the pixel electrode in a case where the level ofthe output signals is greater than or equal to a predetermined level, ina situation where the illuminance is high, the photoelectric converterscan be driven in a voltage region with which the photoelectricconversion efficiency indicates a linear change with respect to a changein the potential difference between the pixel electrode and the oppositeelectrode. It thereby becomes possible to use a wider voltage regionwhile guaranteeing linearity. In addition, power consumption can besuppressed by using a relatively low bias voltage in a standardphotographing mode. In other words, the effects of expanding the dynamicrange by means of electrical control and suppressing power consumptioncan be obtained. In this way, according to the embodiments of thepresent disclosure, sensitivity is adjusted by means of electricalcontrol in accordance with the illuminance, and therefore the effect ofsuppressing power consumption can be obtained while enablingphotographing at a sensitivity that corresponds to the environment inwhich photographing is carried out.

The function of the control circuit 160 may be realized by means of acombination of a general-purpose processing circuit and software, or maybe realized by means of hardware specifically for this kind ofprocessing. It should be noted that, in the example depicted in FIG. 1,the row scanning circuit 120, the detection circuit 130A, the voltagesupply circuit 150, and the control circuit 160 are integrally formed onthe semiconductor substrate 110 on which the plurality of pixels Px arearranged. For example, the control circuit 160 can be an integratedcircuit formed on the semiconductor substrate 110. Due to these circuitsbeing arranged on the semiconductor substrate 110 on which the outputcircuits of each pixel Px are formed, it becomes possible to integrallyform these circuits on the semiconductor substrate 110 together with theoutput circuits of each pixel Px, by applying a process that is similarto the process of forming the output circuits of each pixel Px. However,it is not essential for all of these circuits to be integrally formed onthe semiconductor substrate 110 together with the output circuits ofeach pixel Px. It is also possible for some or all of these circuits tobe arranged on a substrate that is different from the semiconductorsubstrate 110 on which the output circuits of each pixel Px are formed.In this case, the imaging device 100A can be provided in the form of apackage in which the semiconductor substrate 110 on which the pluralityof pixels Px are formed, the row scanning circuit 120, the detectioncircuit 130A, the voltage supply circuit 150, and the control circuit160 are integrated.

In the aforementioned example, the control circuit 160 detects the levelof the output signals from each pixel Px by means of the detectioncircuit 130A, and determines whether the quantity of light incident onthe photoelectric converters is greater than or equal to a predeterminedquantity of light by means of a comparison based on the voltage level ofthe reference line 132. In other words, the control circuit 160 executesa determination in which the voltage level of the reference line 132 isused as a threshold value. However, the method of determining whetherthe quantity of light incident on photoelectric converters is greaterthan or equal to the predetermined quantity of light is not restrictedto this example.

For example, the detection circuit 130A may be configured so as toinclude an analog-digital conversion circuit and to output digital datathat expresses the magnitude of the voltages of the output signal linesS_(j) detected, to the control circuit 160 or the image processingcircuit 164. In this case, a threshold value for determining whether thequantity of light incident on photoelectric converters is greater thanor equal to the predetermined quantity of light can be stored in advancein the memory 162, for example. In a case where, for example, a digitalvalue received from the detection circuit 130A is lower than thethreshold value retained in the memory 162, the control circuit 160determines that the quantity of light incident on the photoelectricconverters is lower than the predetermined quantity of light. Inaddition, the control circuit 160 executes control in which a voltage isapplied to the voltage line 152 to cause the potential differencebetween the opposite electrode and the pixel electrode to be a firstpotential difference that is relatively small. For example, the controlcircuit 160 causes the voltage supply circuit 150 to be driven in such away that the relatively low first voltage V1 is applied to the voltageline 152.

Exemplary Configuration of Pixels Px

FIG. 2 depicts an exemplary circuit configuration of the imaging device100A. Four pixels are extracted from the plurality of pixels Px includedin the imaging region depicted in FIG. 1 and schematically depicted inFIG. 2.

Each pixel Px includes a photoelectric converter 10 and an outputcircuit 20 that is electrically coupled to the photoelectric converter10. In the configuration exemplified in FIG. 2, the output circuit 20includes a signal detection transistor 22, an address transistor 24, anda reset transistor 26. The signal detection transistor 22, the addresstransistor 24, and the reset transistor 26 are typically field-effecttransistors formed on the semiconductor substrate 110, and, hereinafter,an example is described in which N-channel MOS transistors are used asthe transistors unless otherwise particularly specified.

As schematically depicted in FIG. 2, the photoelectric converter 10includes an opposite electrode 11 serving as a first electrode, a pixelelectrode 12 serving as a second electrode, and a photoelectricconversion layer 13 sandwiched between the opposite electrode 11 and thepixel electrode 12. The opposite electrode 11 is transparent. It shouldbe noted that the word “transparent” in the present specification meansthat at least a portion of light of a wavelength that can be absorbed bythe photoelectric conversion layer 13 is transmitted, and it is notessential for light to be transmitted across the entire wavelength rangeof visible light.

As depicted, the opposite electrode 11 of each pixel Px is electricallycoupled to the voltage line 152. Consequently, the voltage supplycircuit 150 is able to selectively apply the first voltage V1 or thesecond voltage V2, for example, collectively to the opposite electrodes11 of the plurality of pixels Px via the voltage line 152. In FIG. 2, itis depicted as if the voltage line 152 is coupled to each oppositeelectrode 11 of the plurality of pixels Px. However, typically, theopposite electrode 11 of each pixel Px is a single transparent electrodethat is continuous among the plurality of pixels Px, and it is notnecessary for the voltage line 152 to be a wire that branches into aplurality.

Meanwhile, the pixel electrode 12 is provided electrically isolated ineach pixel Px. As depicted, the pixel electrode 12 of each pixel Px iscoupled to the gate of the signal detection transistor 22 of thecorresponding output circuit 20. The source of the signal detectiontransistor 22 is coupled to the corresponding output signal line S_(j)via the address transistor 24. The drain of the signal detectiontransistor 22 is coupled to a power source line 32. The power sourceline 32 functions as a source-follower power source due to a powersource voltage VDD of approximately 3.3 V applied during operation.

The gate of the address transistor 24 is coupled to a row signal lineR_(i). The row scanning circuit 120 can switch the address transistors24 between on-state and off-state and can read signals from the pixelsPx of a selected row to an output signal line S_(j), by controlling thevoltage levels applied to the row signal lines Ri.

In this example, the output circuit 20 includes the reset transistor 26.One of the source and the drain of the reset transistor 26 is coupled toa node FD. The node FD electrically couples the photoelectric converter10 to the gate of the signal detection transistor 22. The other of thesource and the drain of the reset transistor 26 is coupled to a resetvoltage line 36. A predetermined reset voltage V_(RST) is applied to thereset voltage line 36 during operation of the imaging device 100A.Typically, as depicted, a reset signal line 46 is coupled in common tothe gates of the reset transistors 26 of the plurality of pixels Pxbelonging to the same row.

In this example, the reset signal line 46 is coupled to the row scanningcircuit 120. The row scanning circuit 120 switches the reset transistors26 to on-state in units of rows of the plurality of pixels Px bycontrolling the voltage level applied to the reset signal line 46. Thus,the potential of the node FD of a pixel Px in which the reset transistor26 has been switched to on-state can be reset to V_(RST). If the voltageapplied to the opposite electrode 11 of each pixel Px from the voltagesupply circuit 150 is taken as V1 or V2, a bias voltage that is appliedbetween the pixel electrode 12 and the opposite electrode 11 immediatelyafter a reset is (V1−V_(RST)) or (V2−V_(RST)). As described hereinafter,in the embodiments of the present disclosure, specific values of thesevoltages can be selected such that (V1−V_(RST))>0 and (V2−V_(RST))>0 aresatisfied.

FIG. 3A depicts an exemplary device structure of a pixel Px. Thesemiconductor substrate 110 has impurity regions 111 to 115 and elementisolation regions 116. The element isolation regions 116 electricallyisolate the output circuit 20 provided in each pixel Px, between thepixels Px. Hereinafter, a P-type silicon substrate is given as anexample of the semiconductor substrate 110. The impurity regions 111 to115 are typically N-type diffusion regions. The semiconductor substrate110 may be an insulating substrate having a semiconductor layer providedon the surface thereof or the like.

The signal detection transistor 22 includes the impurity regions 113 and114 from among the impurity regions 111 to 115, a gate insulation layer22 g on the semiconductor substrate 110, and a gate electrode 22 e onthe gate insulation layer 22 g. The impurity region 113 functions as adrain region of the signal detection transistor 22. The impurity region114 functions as a source region of the signal detection transistor 22.In the configuration depicted, the address transistor 24 shares theimpurity region 114 with the signal detection transistor 22. The addresstransistor 24 includes a gate insulation layer 24 g on the semiconductorsubstrate 110, a gate electrode 24 e on the gate insulation layer 24 g,and the impurity region 115. The impurity region 115 functions as asource region of the address transistor 24.

The reset transistor 26 includes the impurity regions 111 and 112, agate insulation layer 26 g on the semiconductor substrate 110, and agate electrode 26 e on the gate insulation layer 26 g. Although notdepicted in FIG. 3A, the aforementioned reset voltage line 36, forexample, is coupled to the impurity region 112. It should be noted thatthe aforementioned power source line 32 is coupled to the impurityregion 113 serving as the drain region of the signal detectiontransistor 22. An aforementioned output signal line S_(j) is coupled tothe impurity region 115 serving as the source region of the addresstransistor 24. As schematically depicted in FIG. 3A, an elementisolation region 116 is provided between the reset transistor 26 and thesignal detection transistor 22.

An interlayer insulating layer 50 covers the signal detection transistor22, the address transistor 24, and the reset transistor 26 formed on thesemiconductor substrate 110. The photoelectric converter 10 of eachpixel Px is supported by the interlayer insulating layer 50. Theinterlayer insulating layer 50 includes a plurality of insulating layerseach formed from silicon dioxide, for example.

The opposite electrode 11 of the photoelectric converter 10 is locatedat the side where light from an object is incident, and is typicallyformed from a transparent electrically conductive material such as ITO.As mentioned above, the opposite electrode 11 is typically provided inthe form of a single electrode layer that is continuous across theplurality of pixels Px. An optical filter 14 such as a color filter, amicrolens 16 may be arranged on a main surface, at the opposite side ofthe opposite electrode 11 to the photoelectric conversion layer 13.

The photoelectric conversion layer 13 located between the oppositeelectrode 11 and the pixel electrode 12 is formed from an organicmaterial or an inorganic material such as amorphous silicon, andreceives incident light via the opposite electrode 11 and causesexcitons to be generated. The photoelectric conversion layer 13 mayinclude a layer configured from an organic material and a layerconfigured from an inorganic material. Similar to the opposite electrode11, the photoelectric conversion layer 13 is typically provided in theform of a single photoelectric conversion structure that is continuousacross the plurality of pixels Px.

The pixel electrode 12 is located nearer the semiconductor substrate 110than the photoelectric conversion layer 13, and is spatially separatedfrom the pixel electrodes 12 of other adjacent pixels Px and is therebyelectrically isolated therefrom. The pixel electrode 12 can be formedfrom a metal such as aluminum or copper, a metal nitride, polysiliconimparted with conductivity due to being doped with an impurity, forexample.

Each pixel Px has a conductive structure 52 inside the interlayerinsulating layer 50. The conductive structure 52 electrically couplesthe pixel electrode 12 to the output circuit 20 including the signaldetection transistor 22 and the like. The conductive structure 52includes a via formed from a metal such as copper, a plug formed frompolysilicon, or the like, and electrically couples the pixel electrode12 and the impurity region 111 formed in the semiconductor substrate 110to each other, as schematically depicted in FIG. 3A. This conductivestructure 52 is also coupled to the gate electrode 22 e of the signaldetection transistor 22. In other words, the output circuit 20 outputs asignal that corresponds to the potential of the pixel electrode 12 tothe corresponding output signal line S_(j) by means of a source followerthat includes the signal detection transistor 22.

During operation, a potential difference ΔV is applied between theopposite electrode 11 and the pixel electrode 12 as schematicallydepicted in FIG. 3A, due to a predetermined voltage applied to theopposite electrode 11 from the voltage supply circuit 150 via thevoltage line 152. Here, the voltage supply circuit 150 applies a voltageto the opposite electrode 11 such that the potential of the oppositeelectrode 11 becomes higher than the potential of the pixel electrode12, based on the pixel electrode 12. By making the potential of theopposite electrode 11 higher than the potential of the pixel electrode12, from among positive and negative charges generated in thephotoelectric conversion layer 13 due to the incidence of light, chargeshaving a positive polarity, such as electron holes, can be collected bythe pixel electrode 12 as signal charges. Hereinafter, unless otherwisespecified, an example in which electron holes are used as signal chargeswill be described. It should be noted that, in the example depicted inFIG. 3A, an electron blocking layer 13 e is arranged between thephotoelectric conversion layer 13 and the pixel electrode 12, and theinjection of electrons into the pixel electrode 12 from thephotoelectric conversion layer 13 is suppressed. The electron blockinglayer 13 e may have a photoelectric conversion function.

In a typical embodiment of the present disclosure, a first voltage V1and a second voltage V2 with which the potential of the oppositeelectrode 11 becomes higher than the potential of the pixel electrode 12are used in either of a state in which the first voltage V1 is appliedto the voltage line 152 from the voltage supply circuit 150 and a statein which the second voltage V2 is applied to the voltage line 152 fromthe voltage supply circuit 150. It should be noted that the potential ofthe pixel electrode 12 is determined according to the aforementionedreset voltage V_(RST) that is supplied via the reset transistor 26.Consequently, in a typical embodiment of the present disclosure,(V1−V_(RST))>0 and (V2−V_(RST))>0 are satistied. A positive voltage of 0V or in the vicinity of 0 V, for example, is used as the reset voltageV_(RST).

The impurity region 111 is coupled to the conductive structure 52 in theinterlayer insulating layer 50. A P-N junction formed in thesemiconductor substrate 110 by the impurity region 111 functions as acharge accumulation capacitance in which positive charges, such aselectron holes, collected by the pixel electrode 12 are temporarilyaccumulated. In a typical embodiment of the present disclosure, electronholes are used as signal charges, and therefore the potential of theimpurity region 111 serving as a charge accumulation unit increasestogether with the accumulation of signal charges in the impurity region111.

By applying a voltage to the opposite electrode 11 such that thepotential of the opposite electrode 11 becomes lower than that of thepixel electrode 12, it goes without saying that it is also possible forelectrons to be used as signal charges, for example. FIG. 3B is aschematic cross-sectional view for describing an operation of the pixelsPx in a case where electrons are used as signal charges. In a case wherenegative charges are to be collected by the pixel electrode 12, forexample, it is sufficient that a voltage is applied to the oppositeelectrode 11 such that the potential of the pixel electrode 12 becomeshigher than the potential of the opposite electrode 11. In theconfiguration exemplified in FIG. 3B, an electron-hole blocking layer 13h is arranged between the photoelectric conversion layer 13 and thepixel electrode 12, and the injection of electron holes into the pixelelectrode 12 from the photoelectric conversion layer 13 is suppressed.

With this case also, the control circuit 160 causes a predeterminedvoltage to be output from the voltage supply circuit 150 such that thepotential difference applied between the opposite electrode 11 and thepixel electrode 12 becomes the first potential difference, in a casewhere the level of the output signals detected by the detection circuit130A is less than the voltage level of the reference line 132, forexample. Furthermore, in a case where the level of the output signalsdetected by the detection circuit 130A is greater than or equal to thevoltage level of the reference line 132, the control circuit 160 causesa voltage to be output from the voltage supply circuit 150 such that thepotential difference applied between the opposite electrode 11 and thepixel electrode 12 becomes a second potential difference that is greaterthan the first potential difference. It should be noted that, in aconfiguration in which electrons are accumulated as signal charges, thepotential of the impurity region 111 serving as a charge accumulationunit decreases together with the accumulation of signal charges in theimpurity region 111.

Exemplary Photoelectric Conversion Characteristics of PhotoelectricConversion Layer

Here, a description will be given regarding a relationship between thephotoelectric conversion characteristics of the photoelectric conversionlayer 13 and the voltage supplied to the voltage line 152 by the voltagesupply circuit 150. Hereinafter, unless otherwise specified, an examplein which electron holes are used as signal charges will be described.

FIG. 4 depicts a typical example of the photoelectric conversioncharacteristics of the photoelectric conversion layer 13. In FIG. 4, thehorizontal axis represents the potential difference ΔV applied betweenthe opposite electrode 11 and the pixel electrode 12, and the verticalaxis represents the photoelectric conversion efficiency η of thephotoelectric conversion layer 13. Here, the photoelectric conversionefficiency η means the ratio per unit second of the number of chargescollected by the pixel electrode 12, with respect to the number ofphotons incident on the photoelectric converter 10, for one pixel Px. Itshould be noted that the number of charges is a number that is measuredwith elementary electric charge as a unit.

As exemplified in FIG. 4, in the embodiments of the present disclosure,a change is indicated in which the photoelectric conversion efficiency ηof the photoelectric conversion layer 13 generally increases with anupwardly convex curved form with respect to an increase in the potentialdifference ΔV applied between the opposite electrode 11 and the pixelelectrode 12. A photoelectric conversion layer having photoelectricconversion characteristics such as those depicted in FIG. 4 can berealized by using organic photoelectric conversion materials that aregenerally applied in the forming of an organic photoelectric conversionfilm and combinations thereof.

In the example depicted in FIG. 4, the photoelectric conversionefficiency η indicates a comparatively sharp increase with respect to achange in the potential difference ΔV in a voltage region having acomparatively low potential difference ΔV of approximately 0 to 3 V, andindicates a comparatively gentle increase with respect to a change inthe potential difference ΔV in a voltage region having a comparativelyhigh potential difference ΔV of approximately 3 V or more. In thepresent specification, a voltage range in which the photoelectricconversion efficiency η indicates a comparatively sharp increase withrespect to a change in the potential difference ΔV applied between theopposite electrode 11 and the pixel electrode 12 is referred to as afirst voltage range, and a voltage range in which the photoelectricconversion efficiency η indicates a comparatively gentle increase withrespect to a change in the potential difference ΔV is referred to as asecond voltage range.

As depicted in FIG. 4, a change in the level of the signals with respectto a change in the quantity of light incident on the photoelectricconverters 10, in the second voltage range is relatively small comparedto that in the first voltage range, and, in the example depicted in FIG.4, it can be said that the photoelectric converters 10 indicatephotoelectric conversion characteristics that are comparatively flat inthe second voltage range. The second voltage range, for example, can bea voltage region in which a change in the level of the signals withrespect to a change in the quantity of light incident on thephotoelectric converters 10 is 25% or less. “A change in the level ofthe signals with respect to a change in the quantity of incident lightbeing 25% or less” is a change that corresponds to ⅓ of the differencebetween two adjacent levels when converted into InternationalOrganization for Standardization-standards (ISO-standards).

The first voltage range can be defined as a voltage range in which thepotential difference ΔV applied between the opposite electrode 11 andthe pixel electrode 12, in other words, the rate of change in thephotoelectric conversion efficiency of the photoelectric converter 10with respect to the bias voltage, indicates a larger value than when thebias voltage is in the second voltage range. The specific ranges of thefirst voltage range and the second voltage range may differ depending onthe use of the imaging device 100A, the material of the photoelectricconversion layer 13, and the like, but can be defined as describedhereinafter, for example. In a graph of the photoelectric conversionefficiency η of the photoelectric converter 10 with respect to the biasvoltage between the opposite electrode 11 and the pixel electrode 12, asindicated by a dashed line in FIG. 4, a tangent T1 is drawn at a pointwhere the photoelectric conversion efficiency η rises from 0.Furthermore, a tangent T2 is drawn at a point corresponding to thelargest value during operation for the bias voltage. The value of thebias voltage at an intersecting point of these tangents T1 and T2 istaken as Vt, and a voltage range that is less than Vt is taken as thefirst voltage range.

In the example depicted in FIG. 4, the value of the potential differenceΔV where the photoelectric conversion efficiency η rises from 0 is 0 V,and the largest value of the bias voltage during operation is ΔV=12 V.The X coordinate of the intersecting point of the tangents at thesepoints is approximately 3 V, and consequently, as depicted in FIG. 4, avoltage region of approximately 0 V or more and less than 3 V can betaken as the first voltage range, and a voltage region of approximately3 V or more and 12 V or less can be taken as the second voltage range.

However, it is also possible that there is no intersection between thetangent T1 at the point where the photoelectric conversion efficiency ηrises from 0 and the tangent T2 at the point corresponding to thelargest value during operation for the bias voltage, in a case where acharacteristic curve in which the photoelectric conversion efficiency ηrises gently from 0 is obtained in a region in which the potentialdifference ΔV is comparatively small, as exemplified in FIG. 5. In sucha case, in a graph of the photoelectric conversion efficiency η, asindicated by a dashed line in FIG. 5, a tangent T3 is drawn at a point Rwhere the value of the photoelectric conversion efficiency η becomes0.06, and an intersecting point between this tangent T3 and the tangentT2 is obtained. Then, the value of the bias voltage at the intersectingpoint of the tangents T3 and T2 may be taken as Vt, and a voltage rangethat is less than Vt may be taken as the first voltage range.

It should be noted that the aforementioned value 0.06 for thephotoelectric conversion efficiency η is a normalized value when thephotoelectric conversion efficiency η at the point corresponding to thelargest value during operation for the bias voltage is taken as 1. Inthe field of digital cameras, ND filters are sometimes combined in adigital camera for photographing with a low shutter speed or the like.The sensitivity realized by means of the value 0.06 for thephotoelectric conversion efficiency η generally corresponds to the casewhere an ND16 filter is applied. Consequently, in a graph of thephotoelectric conversion efficiency η with respect to the potentialdifference ΔV, Vt is obtained using the tangent at the point R where theY coordinate is 0.06, and thus a sensitivity corresponding to a range ofND2 to ND16, for example, can be realized by means of electricalcontrol.

Alternatively, a voltage range in which a change in the photoelectricconversion efficiency η is less than 10% with respect to a change of 1 Vin the bias voltage may be used as the second voltage range. In thiscase, the second voltage range is determined as being a voltage range inwhich (c−b) constituting an increment in the photoelectric conversionefficiency η satisfies the relationship (c−b)<0.1*b when a first pointP(a, b) and a second point Q(a+1, c) are taken on the graph, as depictedin FIG. 6. Here, “*” in the aforementioned relational expressionrepresents multiplication.

As yet another alternative, the first voltage range or the secondvoltage range can also be determined as described hereinafter. Forexample, in a graph of the photoelectric conversion efficiency η of thephotoelectric converter 10 with respect to the bias voltage between theopposite electrode 11 and the pixel electrode 12, a region in which thephotoelectric conversion efficiency η is 0.7 or more may serve as thesecond voltage range, as depicted in FIG. 7. It should be noted that,when a region in which the photoelectric conversion efficiency η is 0.7or more is defined as the second voltage range, there is an advantage inthat it is easy to achieve correspondence with ISO numerical values. Itis sufficient that specific ranges for the first voltage range and thesecond voltage range are set as appropriate in accordance with the useof the imaging device 100A or the like.

As the aforementioned first voltage V1 and second voltage V2, voltagescan be used with which the photoelectric conversion efficiency ηproduced when the first voltage V1 is supplied to the photoelectricconverter 10 is lower than when the second voltage V2 is supplied to thephotoelectric converter 10. As mentioned above, the photoelectricconversion efficiency η in the photoelectric conversion layer 13,typically, generally increases in a monotonous manner with respect to anincrease in the potential difference ΔV applied between the oppositeelectrode 11 and the pixel electrode 12. In a typical embodiment of thepresent disclosure, voltages in the second voltage range are used as thefirst voltage V1 and the second voltage V2. Hereinafter, a descriptionwill be given regarding an operation example of the imaging device 100Awhen voltages in the second voltage range are used as the first voltageV1 and the second voltage V2.

Operation Example of Imaging Device 100A

Here, the photoelectric conversion efficiency η in the photoelectricconversion layer 13 is assumed to indicate a change such as thatdepicted in FIG. 4 with respect to an increase in the potentialdifference ΔV applied between the opposite electrode 11 and the pixelelectrode 12, and the value Vt of the bias voltage at the aforementionedintersecting point between the tangents T1 and T2 is assumed to be 3 V.At such time, when a voltage region of less than 3 V is taken as thefirst voltage range and a voltage region of 3 V or more and 12 V or lessis determined as the second voltage range, for example, a voltage of 6 Vcan be used as the first voltage V1 and a voltage of 12 V can be used asthe second voltage V2, for example.

In a case where definitions such as these are adopted for the firstvoltage range and the second voltage range, the ratio of thephotoelectric conversion efficiency η produced when the second voltageV2 is applied to the opposite electrode 11 with respect to the value ofthe photoelectric conversion efficiency η produced when the firstvoltage V1 is applied to the opposite electrode 11 is, typically,greater than 1 and 1.25 or less. In this example, the photoelectricconversion efficiency η produced when the first voltage V1 is applied tothe opposite electrode 11 is approximately 0.87, the value of thephotoelectric conversion efficiency η produced when the second voltageV2 is applied is approximately 1.0, and the value of the ratio for thesevalues for η is approximately 1.15. It should be noted that 2, which isthe value of the ratio (V2/V1) of the second voltage V2 with respect tothe first voltage V1, is greater than the aforementioned ratio value1.15 in relation to η.

FIG. 8 is a schematic flowchart depicting a first exemplary operation ofthe imaging device 100A. In the example depicted in FIG. 8, first, it isdetermined whether or not the quantity of light incident on thephotoelectric converters 10 is greater than or equal to a predeterminedquantity of light (step S1). For example, the level of the signals thatare output to the output signal lines S_(j) from the output circuits 20is detected by the detection circuit 130A. In a case where the detectedlevel is greater than or equal to the voltage level of the referenceline 132 serving as a threshold value, it can be determined that thequantity of light incident on the photoelectric converters 10 is greaterthan or equal to the predetermined quantity of light. The level of thesignals from the output circuits 20 may be detected by, for example,when the user has half-pressed a release button, switching the addresstransistors 24 of some of the pixels Px to on, and causing a voltagethat corresponds to the illuminance to be output from the outputcircuits 20. Alternatively, the level of the signals detected by thedetection circuit 130A in, for example, the frame immediately precedingthe frame in which images are to be acquired from thereon may be used.

It goes without saying that the method of determining whether or not thequantity of light incident on the photoelectric converters 10 is greaterthan or equal to the predetermined quantity of light is not restrictedto a specific method, and various methods can be adopted. For example,the level of the signals detected by the detection circuit 130A may beconverted into a digital value by an analog-digital conversion circuit,and whether or not the quantity of light incident on the photoelectricconverters 10 is greater than or equal to the predetermined quantity oflight may be determined by comparison with a threshold value stored inadvance in the memory 162. Whether or not the quantity of light incidenton the photoelectric converters 10 is greater than or equal to thepredetermined quantity of light can be determined by the control circuit160 or the image processing circuit 164, for example. The controlcircuit 160 may include a logic circuit formed on the semiconductorsubstrate 110. Whether or not the quantity of light incident on thephotoelectric converters 10 is greater than or equal to thepredetermined quantity of light may be determined by an ISP, forexample, arranged outside of the imaging device 100A.

In a case where it has been determined that the quantity of lightincident on the photoelectric converters 10 is less than thepredetermined quantity of light, a voltage is applied to thephotoelectric converters 10 in such a way that the potential differencebetween the opposite electrode 11 and the pixel electrode 12 becomes thefirst potential difference (step S2). The control circuit 160 supplies adrive signal to the voltage supply circuit 150, and, for example, causesthe first voltage V1 to be applied to the voltage line 152 from thevoltage supply circuit 150. In other words, here, in a situation wherethe illuminance is low, the bias voltage between the pixel electrode 12and the opposite electrode 11 is made to be relatively low.

At the standard setting, the effect of suppressing power consumption canbe expected by applying an operation with which the relatively low firstvoltage V1 is used as the voltage supplied to the photoelectricconverters 10 from the voltage supply circuit 150. The state in whichthe first voltage V1 in the second voltage range is being supplied fromthe voltage supply circuit 150 may be referred to as a standard mode.Furthermore, using the relatively low first voltage V1 at the standardsetting is not only power saving but is also advantageous for increasingoperation speed compared to using the second voltage V2 at the standardsetting.

Japanese Patent No. 6202512, for example, discloses a technique forrealizing a global shutter with pixel sensitivity being substantially 0by bringing a potential difference applied between an opposite electrodeand a pixel electrode arranged on either side of a photoelectricconversion layer near to 0 V. In a case where this kind of technique isapplied, the time required for switching voltages becomes longer whenthere is a large difference between the voltage applied to the oppositeelectrode during exposure, and the voltage applied to the oppositeelectrode when pixel sensitivity is set to 0 for a state to be enteredin which the shutter is electronically closed. In contrast, when thereis a small difference between voltages applied to the opposite electrodeduring exposure and during shutter use, the time required for switchingvoltages becomes shorter, and it becomes possible to execute a shutteroperation at a higher speed. Furthermore, it is possible to shorten thetime required from the end of exposure, in other words, from the voltageapplied to the opposite electrode being decreased to approximately 0 V,to signal reading, and therefore driving in which the relatively lowfirst voltage V1 is used at the standard setting is particularlyadvantageous for applying an electrical global shutter. The contentdisclosed in Japanese Patent No. 6202512 is incorporated herein in itsentirety for reference.

FIGS. 9 and 10 are schematic cross-sectional views for describing anoperation of the pixels Px when a voltage of 6 V is applied as the firstvoltage V1 to the opposite electrode 11. During operation, the potentialdifference ΔV is applied between the opposite electrode 11 and the pixelelectrode 12. The reset voltage V_(RST) is a voltage in the vicinity of0 V, for example, and consequently, in a state in which the voltagesupply circuit 150 is supplying the first voltage V1, the photoelectricconversion layer 13 is in a state in which a potential difference ofapproximately 6 V is applied, as schematically depicted in FIG. 9.

When light is incident on the photoelectric conversion layer 13 andcharges are generated inside the photoelectric conversion layer 13,these charges move according to the electric field between the oppositeelectrode 11 and the pixel electrode 12. As schematically depicted inFIG. 9, positive charges are accumulated in the impurity region 111serving as a charge accumulation unit via the conductive structure 52,and negative charges are discharged to the voltage line 152 from thephotoelectric conversion layer 13 via the opposite electrode 11.

Here, as schematically depicted by the arrows hν in FIG. 10, it isassumed that the accumulation of signal charges has continued at arelatively high illuminance in a state in which the first voltage V1 isbeing supplied from the voltage supply circuit 150. When theaccumulation of signal charges in the impurity region 111 continues,since positive charges are used as signal charges here, the potential ofthe impurity region 111 gradually increases. Therefore, the effectivebias voltage according to the photoelectric conversion layer 13 is lessthan the actual value of the first voltage V1, and can becomeapproximately 5 V, for example. In other words, high-voltage elementsand element isolation regions are not required, and reliability can beimproved. It should be noted that positive charges produced by the pixelelectrode 12 are no longer collected when the potential of the pixelelectrode 12 exceeds the potential of the opposite electrode 11, andtherefore the potential of the impurity region 111 basically does notexceed the value of the first voltage V1.

Reference will once again be made to FIG. 8. In step S1, in a case whereit has been determined that the quantity of light incident on thephotoelectric converters 10 is greater than or equal to thepredetermined quantity of light, a voltage is applied to thephotoelectric converters 10 in such a way that the potential differencebetween the opposite electrode 11 and the pixel electrode 12 becomes asecond potential difference that is greater than the first potentialdifference (step S3). The control circuit 160 supplies a drive signal tothe voltage supply circuit 150, and, for example, causes the secondvoltage V2, which is higher than the first voltage V1, to be applied tothe voltage line 152 from the voltage supply circuit 150.

When the potential difference ΔV between the opposite electrode 11 andthe pixel electrode 12 increases, the electric field inside thephotoelectric conversion layer 13 increases, and a larger quantity ofpositive charges are collected by the pixel electrode 12, asschematically depicted in FIG. 11. Here, a voltage of 12 V is used asthe second voltage V2. As is apparent with reference to FIG. 4, thephotoelectric conversion efficiency in a state in which the secondvoltage V2 is applied to the opposite electrode 11 is high compared to astate in which the first voltage V1 is applied to the opposite electrode11. In other words, the sensitivity of the pixels Px obtained when thesecond voltage V2 is applied to the opposite electrode 11 is in a highstate compared to a state in which the first voltage V1 is applied tothe opposite electrode 11.

The potential of the impurity region 111 gradually rises due tocontinuation of the accumulation of signal charges in the impurityregion 111, which is similar to when the first voltage V1 is applied tothe opposite electrode 11. Consequently, the effective bias voltageaccording to the photoelectric conversion layer 13 is less than theactual value of the second voltage V2, and can become approximately 11V, for example, as depicted in FIG. 11.

FIG. 12 schematically depicts a typical example of a change in the levelof the signals from the output circuits 20, with respect to a change inthe quantity of light incident on the photoelectric converters 10, whenthe first voltage V1 is applied to the opposite electrode 11, and whenthe second voltage V2 is applied to the opposite electrode 11. A line G1in FIG. 12 depicts a change in the level of the output signals when avoltage of 6 V is applied as the first voltage V1 to the oppositeelectrode 11, and G2 depicts a change in the level of the output signalswhen a voltage of 12 V is applied as the second voltage V2 to theopposite electrode 11.

In the example of FIG. 12, the level of the signals from the outputcircuits 20 indicates a linear change with respect to a change in thequantity of light incident on the photoelectric converters 10, in eitherof a state in which a voltage of 6 V is applied as the first voltage V1to the opposite electrode 11 and a state in which a relatively highvoltage of 12 V is applied as the second voltage V2 to the oppositeelectrode 11. In other words, it is understood that it is possible toensure linearity of the signal output with respect to a change inilluminance when either of the first voltage V1 and the second voltageV2 is supplied from the voltage supply circuit 150.

However, in the example depicted in FIG. 12, in a case where the firstvoltage V1 is applied to the opposite electrode 11, the range in whichthe signal output with respect to a change in illuminance indicates alinear change is narrow compared to the case where the second voltage V2is applied to the opposite electrode 11. This is because the rate ofchange in the signal output with respect to a change in illuminance canadopt a larger value when the first voltage V1 is applied to theopposite electrode 11.

FIG. 13 depicts a typical example of the photoelectric conversioncharacteristics of the photoelectric conversion layer 13. The graph inFIG. 13 is the same as the graph depicted in FIG. 4. In the exampledepicted in FIG. 13, the inclination of the graph line increases as thepotential difference ΔV decreases. In a case where the photoelectricconverters 10 indicate photoelectric conversion characteristics such asthis, when the potential of the impurity region 111 increases due to theaccumulation of signal charges with, for example, the point where thepotential difference ΔV is 6 V as a starting point, the potentialdifference ΔV approaches the first voltage range in which the graphindicates a larger inclination. As a result, a graph indicating changein the signal output with respect to a change in illuminance may deviatefrom a straight line. In other words, the linearity may collapse whenilluminance exceeded a range while the relatively low first voltage V1is applied to the opposite electrode 11.

In contrast, in a state in which the relatively high second voltage V2is applied to the opposite electrode 11, as depicted in FIG. 13, therate of change in the photoelectric conversion efficiency η with respectto a change in the potential difference ΔV is relatively small, and,consequently, it becomes possible to permit a larger change for thepotential difference ΔV. For example, the range for the potentialdifference ΔV that imparts a change Δη in η of the same magnitude can beapproximately tripled. In other words, in a state in which therelatively high second voltage V2 is applied to the opposite electrode11, as depicted in FIG. 12, the range for the quantity of light withwhich the level of the output signals changes in a linear manner can beapproximately tripled compared to when the first voltage V1 is appliedto the opposite electrode 11. To paraphrase this, in a state in whichthe second voltage V2 is applied to the opposite electrode 11, itbecomes possible to permit a range that is approximately tripled for thequantity of light compared to when the first voltage V1 is applied tothe opposite electrode 11, which is advantageous for photographing abright scene requiring a wider dynamic range.

In this way, control is carried out in such a way that the first voltageV1 in the second voltage range is supplied to the photoelectricconverters 10 in an environment in which illuminance is comparativelylow, and the higher second voltage V2 is supplied to the photoelectricconverters 10 in an environment in which illuminance is comparativelyhigh. According to this kind of control, the dynamic range can bechanged in a dynamic manner according to changes in illuminance. Forexample, at the standard setting, the first voltage V1 in the secondvoltage range can be used as the voltage supplied to the photoelectricconverters 10, and, in an environment in which illuminance iscomparatively high, the relatively high second voltage V2 can be used asthe voltage supplied to the photoelectric converters 10. According tothis kind of control, in an environment in which illuminance iscomparatively high, the photoelectric converters 10 can be driven in avoltage region in which the rate of change in the photoelectricconversion efficiency η with respect to the bias voltage is relativelysmall, and it becomes possible to ensure linearity in a wider range. Inother words, it becomes possible to automatically expand the dynamicrange by means of electrical control. Furthermore, the advantage of lowpower consumption can be obtained by adopting, as the standard setting,an operation with which the relatively low first voltage V1 is used asthe voltage supplied to the photoelectric converters 10 from the voltagesupply circuit 150.

As exemplified in FIG. 14, a third electrode 15 may be arranged betweentwo pixel electrodes 12 that are adjacent to each other. As describedhereinafter, by controlling the potential of the third electrode 15, itis possible to further expand the dynamic range relating to thedirection in which the illuminance is high.

FIG. 14 depicts two pixels Px1 and Px2 that are adjacent to each otherin a row or column, for example, of the plurality of pixels Px.Furthermore, in FIG. 14, the third electrode 15 is arranged between thepixel electrode 12 of the pixel Px1 and the pixel electrode 12 of thepixel Px2, and in the same layer as these pixel electrodes 12. The thirdelectrode 15 is spatially separated from the pixel electrode 12 of thepixel Px1 and the pixel electrode 12 of the pixel Px2, and is therebyelectrically isolated from these pixel electrodes 12. The thirdelectrode 15 is configured so that a predetermined voltage can beapplied during operation of the imaging device 100A by being coupled toa power source that is not depicted.

FIG. 15 depicts an example of the arrangement relationship between thepixel electrode 12 and the third electrode 15, when seen from theopposite electrode 11 side. In this example, the third electrode 15 hasa rectangular shape surrounding the pixel electrode 12, and is providedin each of the pixel Px1 and the pixel Px2. It should be noted that itis not essential for the third electrode 15 to be arranged separatelyfor each pixel Px. For example, it is also possible for a single thirdelectrode 15 that straddles the plurality of pixels Px to be providedfor each row of the plurality of pixels Px. Furthermore, it is alsopossible for a grid-shaped third electrode 15 to be arranged across theplurality of pixels Px.

When a potential that is lower than that of the opposite electrode 11 isapplied, the pixel electrode 12 collects positive charges in a regionR1, of the photoelectric conversion layer 13, located more or lessdirectly above the pixel electrode 12, as schematically depicted by theshading in FIG. 15. Similarly, when a potential that is lower than thatof the opposite electrode 11 is applied, the third electrode 15 cancollect positive charges in a region R2, of the photoelectric conversionlayer 13, located more or less directly above the third electrode 15.

Consequently, when the illuminance is high, a voltage that is less thanor equal to the reset voltage V_(RST), for example, is applied to thethird electrode 15 for a potential difference that is greater than orequal to ΔV to be applied to a portion, of the photoelectric conversionlayer 13, located between the opposite electrode 11 and the thirdelectrode 15, and it thereby becomes possible for charges generated nearboundaries of the pixels Px to be preferentially collected by the thirdelectrode 15, as schematically depicted in FIG. 16. As a result, thenumber of charges that reach the pixel electrode 12 decreases, and theeffective photoelectric conversion efficiency can be lowered. In otherwords, it is possible to further expand the dynamic range relating tothe direction in which the illuminance is high. Furthermore, in aconfiguration in which a color filter is arranged on each pixel Px, aneffect of suppressing color mixing can also be obtained. The voltageapplied to the third electrode 15 may be supplied from the voltagesupply circuit 150.

As already described, in a configuration in which electron holes areused as signal charges, together with exposure, there is an increase inthe electron holes accumulated in the impurity region 111 serving as acharge accumulation unit, and therefore the potential of the impurityregion 111 gradually rises. Since the potential of the impurity region111 gradually rises together with exposure, the effective bias voltageaccording to the photoelectric conversion layer 13 becomes less than thevalue of the second voltage V2 even when the second voltage V2 isapplied. Similar to when the illuminance is low with the first voltageV1 applied to the photoelectric converters 10, in this case also, thepotential of the impurity region 111 basically does not exceed thesecond voltage V2. In other words, it is possible to suppress anincrease in the electric field applied to the impurity region 111, whilealso having a comparatively large value for the potential difference ΔVbetween the opposite electrode 11 and the pixel electrode 12.Consequently, a high breakdown voltage is not required at portions suchas the P-N junction formed between the impurity region 111 and regionsoutside thereof or the gate insulation layer 22 g of the signaldetection transistor 22, and reliability is easily ensured.

Example of Output Circuit

FIGS. 17 and 18 schematically depict the relationship between a changein the potential of the node FD that accompanies the accumulation ofsignal charges, and the power source voltage. FIG. 17 schematicallydepicts the potential of a node at the drain side and the source side ofthe reset transistor 26 when a reset is performed. As depicted in FIG.17, due to the reset transistor 26 being set to on-state when thephotoelectric converter 10 is reset, the potential of the node FDconstituting one side out of the drain and the source of the resettransistor 26 matches the potential V_(RST) of the reset voltage line 36constituting the other side.

FIG. 18 schematically depicts the potential of the node FD in a state inwhich signal charges are accumulated after the reset transistor 26 hasbeen set to off-state. As depicted in FIG. 18, the potential of the nodeFD after the accumulation of signal charges rises from the V_(RST) by anamount proportional to a voltage V_(SIG) that corresponds to thequantity of accumulated signal charges Cg. Here, in an environment inwhich illuminance is comparatively high, in particular, in a case wherethe comparatively high second voltage V2 in the second voltage range isbeing supplied to the photoelectric converter 10, the potential of thenode FD may exceed the power source voltage VDD due to the accumulationof electron holes serving as the signal charges Cg.

FIG. 19 depicts a modified example of the output circuit included in thepixels Px. For simplicity, here, a pixel located in the i^(th) row andthe j^(th) column is extracted and depicted from among the plurality ofpixels Px.

In the example exemplified in FIG. 19, the pixel Px has an outputcircuit 20A that is coupled to the photoelectric converter 10. Theoutput circuit 20A, in addition to the signal detection transistor 22,the address transistor 24, and the reset transistor 26, also has a firstcapacitor 241, one electrode of which is coupled to, out of the drainand the source of the reset transistor 26, the side that is not coupledto the pixel electrode 12 of the photoelectric converter 10.

As depicted, an accumulation control line 251 is coupled to, out of theelectrodes of the first capacitor 241, the electrode at the side notcoupled to the reset transistor 26. The accumulation control line 251 iscoupled to an undepicted voltage supply circuit or the like, and therebyapplies a predetermined voltage to the first capacitor 241 duringoperation. It should be noted that, in this example, the output circuit20A also includes a second capacitor 242 that is coupled in parallel tothe reset transistor 26. The first capacitor 241 typically has acapacitance value that is larger than that of the second capacitor 242.

As mentioned above, in an environment in which illuminance is high, thepotential of the node FD may exceed the power source voltage VDD due tothe accumulation of the signal charges Cg. When the potential of thenode FD exceeds the power source voltage VDD, the reading of signals bymeans of a source follower cannot be executed. However, according to theoutput circuit 20A exemplified in FIG. 19, the reset transistor 26 canbe set to on-state when a signal is read after exposure in a mode inwhich, for example, the comparatively high second voltage V2 in thesecond voltage range is applied to the opposite electrode 11. Due to thereset transistor 26 being set to on-state when a signal is read afterexposure, the first capacitor 241 is coupled to the node FD via thereset transistor 26. Due to the first capacitor 241 being coupled to thenode FD via the reset transistor 26, the potential of the node FD can belowered to a level that is less than the VDD, as schematically depictedin FIG. 20. Consequently, it becomes possible to read a signal thatcorresponds to the potential of the pixel electrode 12 that has changeddue to the accumulation of charges generated by photoelectricconversion, without boosting the power source voltage VDD. Here, inFIGS. 19 and 20, out of the drain and the source of the reset transistor26, a node at the side not coupled to the photoelectric converter 10 isreferred to as a node RD.

In this way, in a mode in which a capacitor having a comparatively largecapacitance value is coupled to the node FD via the reset transistor 26serving as a switching element and the potential difference between theopposite electrode 11 and the pixel electrode 12 is increased, forexample, control may be applied in which the reset transistor 26 is setto on-state when a signal that corresponds to accumulated signal chargesis read. According to this kind of control, the potential of the node FDcan be temporarily decreased in a selective manner when a signal thatcorresponds to accumulated signal charges is read, and signal readingcan be executed even in an environment in which illuminance is highwithout using an even higher power source voltage. It should be notedthat a temporary decrease in the potential of the node FD produced bysetting the reset transistor 26 to on-state may be ordinarily executedwhen a signal is read in a mode in which the potential differencebetween the opposite electrode 11 and the pixel electrode 12 isincreased, or may be selectively executed in a case where the potentialof the node FD has exceeded the power source voltage VDD. Alternatively,control can also be applied in which, first, signals are read in a statein which the reset transistor 26 is off-state, and, next, signals areread with the reset transistor 26 being set to on-state. In this case,two items of data are obtained corresponding to two instances of signalreading, and therefore one item of data may be selectively used or thetwo items of data may be combined and used to construct an image.

It should be noted that, in the example depicted in FIG. 19, aninverting amplifier 224 is arranged in each column of the plurality ofpixels Px. An inverting input terminal of the inverting amplifier 224 iscoupled to an output signal line S_(j), and the predetermined referencevoltage V_(ref) is applied to a non-inverting input terminal duringoperation. As depicted, here, the reset voltage line 36 is coupled to anoutput terminal of the inverting amplifier 224.

Furthermore, the output circuit 20A further includes a band controltransistor 28 that is coupled between the reset transistor 26 and thereset voltage line 36. A band control signal line 48 is coupled to thegate of the band control transistor 28. The band control signal line 48is coupled to the row scanning circuit 120, for example, and thepotential thereof is thereby controlled.

According to this kind of configuration, it is possible not only to havethe reset transistor 26 function as a transistor for gain switching butalso to form a feedback loop in which some or all of the output signalsof the signal detection transistor 22 are electrically returned bycontrolling the potential of the reset signal line 46 and the bandcontrol signal line 48. By forming a feedback loop, it is possible toreduce the effect of kTC noise generated due to the reset transistor 26and the band control transistor 28 being off. The details of this kindof noise cancellation for which returning is used are described inJapanese Unexamined Patent Application Publication No. 2017-046333. Thecontent disclosed in Japanese Unexamined Patent Application PublicationNo. 2017-046333 is incorporated herein in its entirety for reference.

FIG. 21 depicts a second modified example of the output circuit includedin the pixels Px. Compared to the configuration described with referenceto FIG. 19, an output circuit 20B depicted in FIG. 21 further includes aset of a signal detection transistor 22 a and an address transistor 24a. As depicted, the set of the signal detection transistor 22 a and theaddress transistor 24 a is coupled in parallel to a set of the signaldetection transistor 22 and the address transistor 24. To be precise,the gate of the signal detection transistor 22 a is coupled to the nodeFD, and the source of the address transistor 24 a is coupled to anoutput signal line S_(j).

The gate of the signal detection transistor 22 and the gate of thesignal detection transistor 22 a are both coupled to the node FD. Incontrast, the drain of the signal detection transistor 22 and the drainof the signal detection transistor 22 a are, for example, each coupledto separate voltage lines, and it thereby becomes possible to applymutually different voltages during operation of the imaging device 100A.In this example, during operation of the imaging device 100A, the VDDserving as a third voltage is applied to the drain of the signaldetection transistor 22, and a fourth voltage VDD2 that is higher thanthe VDD is applied to the drain of the signal detection transistor 22 a.

In the example depicted, a row signal line Ra_(i) is coupled to the gateof the address transistor 24 a. The row signal line Ra_(i) is coupled tothe row scanning circuit 120 in a manner similar to the row signal lineRi, for example, and the row scanning circuit 120 is thereby able toswitch the address transistor 24 a on and off by controlling thepotential of the row signal line Ra_(i), and read a potentialcorresponding to the amount of charge accumulated in the node FD to theoutput signal line S_(j) via the signal detection transistor 22 a andthe address transistor 24 a.

According to the output circuit 20B exemplified in FIG. 21, it ispossible for the signal detection transistor 22 a, to which the higherfourth voltage VDD2 is applied, to be used as a source follower. Forexample, in a case such as where the potential of the node FD exceedsthe power source voltage VDD, the control circuit 160 can cause the rowscanning circuit 120 to be driven in such a way that the addresstransistor 24 is set to off-state and the address transistor 24 a is setto on-state, when a signal is read.

In this way, which of two source followers having mutually differentmagnitudes for source follower power sources is to be used to carry outsignal reading may be switched in accordance with the potential of thenode FD. According to this kind of configuration, signal reading becomespossible even in a case where the potential of the node FD exceeds thepower source voltage VDD. It should be noted that, instead of mutuallyvarying the voltages applied to the drains, transistors having mutuallydifferent threshold voltages may be used as the signal detectiontransistor 22 and the signal detection transistor 22 a. In this case,the aforementioned effect similar to the case where a plurality ofsource followers are provided can be obtained while the voltage appliedto the drains is made common. Furthermore, instead of providing aplurality of source followers, the voltage to be applied to the drain ofthe signal detection transistor 22 may be switched between a thirdvoltage and a fourth voltage in accordance with the potential of thenode FD.

FIG. 22 depicts a third modified example of the output circuit includedin the pixels Px. An output circuit 20C depicted in FIG. 22 has a thirdcapacitor 243 having one electrode coupled to the node FD. An undepictedvoltage supply circuit, for example, is coupled to the other electrodeof the third capacitor 243, and a pulse voltage Cp, for example, isapplied to the other electrode of the third capacitor 243 when a signalthat corresponds to signal charges accumulated in the node FD is read.

By applying the pulse voltage Cp, the potential of the node FD can betemporarily lowered by means of coupling by way of the third capacitor243. Therefore, when a signal is read, the potential of the node FD canbe selectively decreased for the potential of the node FD to be a levelthat is less than the VDD, with the quantity of signal chargesaccumulated in the node FD being retained. That is, even in a case suchas where the potential of the node FD exceeds the power source voltage,it becomes possible to read a signal by way of the signal detectiontransistor 22 without boosting the power source voltage.

FIG. 23 depicts a fourth modified example of the output circuit includedin the pixels Px. An output circuit 20D depicted in FIG. 23 has anattenuator 225 that is coupled between the photoelectric converter 10and the gate of the signal detection transistor 22.

FIG. 24 depicts a specific example of the attenuator 225 depicted inFIG. 23. In the configuration exemplified in FIG. 24, the attenuator 225has a capacitor 228 and a gain control transistor 226 that serves as aswitching element coupled in parallel to the capacitor 228.

During operation, a gain control signal Gc is applied from the rowscanning circuit 120, for example, to the gate of the gain controltransistor 226. For example, in a case such as where the potential ofthe node FD exceeds the power source voltage VDD, the control circuit160 can cause the row scanning circuit 120 to be driven in such a waythat the gain control transistor 226 is set to off-state, when a signalis read. Due to the gain control transistor 226 being set to off-state,the capacitor 228 is coupled to the node FD, and the capacitance valueof the entire node FD can be increased. In other words, the attenuator225 can attenuate the voltage applied to the gate of the signaldetection transistor 22, by a predetermined proportion, and itconsequently becomes possible to read a signal by way of the signaldetection transistor 22 without boosting the power source voltage. Inthe present specification, the term “attenuator” is not restricted to acircuit element that is realized in combination with a switching elementand a capacitor for smoothing, and is interpreted as broadly includingalso a level shifter, a gain amplifier, and the like.

Use of Voltage in First Voltage Range

In the aforementioned FIG. 12, a line G0 indicating a change in thelevel of the output signals with respect to a change in the quantity oflight, produced when a voltage of 2 V is applied to the oppositeelectrode 11, is depicted as a dashed line together with lines G1 andG2. From FIG. 12, in a region in which the quantity of light iscomparatively small when a voltage selected from the first voltage rangeis applied to the opposite electrode 11, the level of the signalsindicates a linear change with respect to a change in the quantity oflight, and it is understood that linearity can be ensured. When thequantity of light increases further, the degree of the increase in thelevel of the signals with respect to the increase in the quantity oflight decreases, and a graph depicting a change in the level of thesignals with respect to a change in the quantity of light comes toindicate a change having a curved form. This means that, in a state inwhich a voltage selected from the first voltage range is applied to theopposite electrode 11, the level of the signals automatically decreasesin accordance with an increase in the quantity of light. In other words,the dynamic range relating to the direction in which the illuminance ishigh is expanded. Using this, as described hereinafter, the dynamicrange relating to the direction in which the illuminance is high can beexpanded compared to a case where the level of the signals changes in alinear form in accordance with an increase in the quantity of light.

Referring to the line G0, in a region in which the illuminance ishigher, there is an increase in the deviation from a straight line in aline depicting a change in the level of the signals with respect to achange in the quantity of light. This is because, as the potentialdifference ΔV decreases, effects such as a decrease in charge pairsgenerated by photoelectric conversion and an increase in thedisappearance of charge pairs due to recombination appear more easily.

However, by obtaining a characteristic curve such as that depicted inFIG. 12 in advance, it becomes possible to carry out an appropriatecorrection to the level of the signals detected by the detection circuit130A. For example, correction coefficients corresponding to quantitiesof light may be stored in the memory 162 in advance in the form of atable, for example, and the pixel value of each pixel Px may bedetermined by multiplying by a correction coefficient. Due to this kindof correction, linearity is compensated, and it becomes possible tofurther expand the dynamic range relating to the direction in which theilluminance is high. For example, compared to the case where the levelof the signals changes in a linear form in accordance with an increasein the quantity of light, the dynamic range relating to the direction inwhich the illuminance is high can be approximately tripled. For example,control may be executed in such a way that the first voltage V1 in thefirst voltage range is supplied to the photoelectric converters 10 in anenvironment in which illuminance is comparatively high, and the secondvoltage V2 in the second voltage range is supplied to the photoelectricconverters 10 in an environment in which illuminance is comparativelylow.

A correction for the level of the signals detected can be executed bythe image processing circuit 164. The function of the image processingcircuit 164, similar to the control circuit 160, may be realized bymeans either of a combination of a general-purpose processing circuitand software, and hardware specifically for image processing. Acorrection for the level of the signals detected may be executed by thecontrol circuit 160.

According to control with which the first voltage V1 in the firstvoltage range is supplied to the photoelectric converters 10 in anenvironment in which illuminance is comparatively high, and the secondvoltage V2 in the second voltage range is supplied to the photoelectricconverters 10 in an environment in which illuminance is comparativelylow, sensitivity can be changed dynamically in accordance with a changein illuminance. For example, at the standard setting, the second voltageV2 in the second voltage range is used as the voltage supplied to thephotoelectric converters 10, and, in an environment in which illuminanceis comparatively high, the first voltage V1 in the first voltage rangeis used as the voltage supplied to the photoelectric converters 10, andit thereby becomes possible for sensitivity to be decreasedautomatically. In addition, in a state in which illuminance iscomparatively high and the first voltage V1 in the first voltage rangeis supplied to the photoelectric converters 10, when the illuminancefurther increases, the potential difference ΔV reduces in accordancewith the accumulation of electron holes in the impurity region 111. As aresult, the photoelectric conversion efficiency η changes in a furtherdecreasing direction, and therefore the dynamic range relating to thedirection in which the illuminance is high can be further expanded.

In this way, it becomes possible to realize an ND filter function so tospeak by means of electrical control, by using a voltage in the firstvoltage range as the first voltage V1. Consequently, it is no longernecessary to prepare a plurality of ND filters even for a photographingscene for which it has heretofore been necessary for one appropriate NDfilter to be selected and used from among a plurality of ND filters, andthe effect of simplifying photographic equipment can be obtained. Forexample, it becomes possible to also implement continuous alteration, inother words, stepless control, of sensitivity that was not possible witha conventional silicon image sensor, and it is possible to increase thedegree of freedom of photographing that corresponds to the scene.

Modified Examples

FIG. 25 depicts an exemplary circuit configuration of an imaging deviceaccording to a modified example of the first embodiment. Compared to theconfiguration of the imaging device 100A described with reference toFIG. 1, an imaging device 1006 depicted in FIG. 25 has a detectioncircuit 1306 instead of the detection circuit 130A. The detectioncircuit 130B does not have the comparator 134.

The detection circuit 130B, for example, includes an analog-digitalconversion circuit, and outputs digital data expressing the magnitudesof the voltages of the output signal lines S_(j) detected, to thecontrol circuit 160. The control circuit 160 determines whether or notthe level of a signal that is output from the output circuit 20 of eachpixel Px is greater than or equal to a predetermined level, on the basisof input from the detection circuit 1306. A threshold value constitutinga basis for the determination can be stored in advance in the memory162, for example. In a case where, for example, a digital value receivedfrom the detection circuit 130B is less than the threshold valueretained in the memory 162, the control circuit 160 determines that thequantity of light incident on the photoelectric converters 10 is lessthan the predetermined quantity of light, and causes the voltage supplycircuit 150 to be driven in such a way that the relatively low firstvoltage V1 is applied to the voltage line 152. According to such aconfiguration, it is possible to reduce the area taken up by thedetection circuit 130B on the semiconductor substrate 110 compared tothe case where the comparator 134 is arranged inside the detectioncircuit. It should be noted that whether or not the quantity of lightincident on the photoelectric converters 10 is greater than or equal tothe predetermined quantity of light may be determined by the imageprocessing circuit 164.

In the aforementioned examples, the voltage applied to the oppositeelectrode 11 of the photoelectric converters 10 is switched between thefirst voltage V1 and the second voltage V2 in accordance with theilluminance. However, the subject for switching the applied voltage isnot restricted to the opposite electrode 11, and the voltage applied tothe pixel electrode 12 may be switched between two voltages, asdescribed hereinafter.

FIG. 26 depicts an exemplary circuit configuration of an imaging deviceaccording to another modified example of the first embodiment. The maindifference between the circuit configuration of an imaging device 100Cdepicted in FIG. 26 and the circuit configuration of the imaging device100A described with reference to FIG. 2 is that, in the imaging device100C, the voltage supply circuit 150 that supplies the first voltage V1and the second voltage V2 is coupled to the reset voltage line 36. Inother words, in this example, at least two mutually different voltagesare selectively supplied as the reset voltage V_(RST) to the resetvoltage line 36. It should be noted that a second voltage supply circuit154 is coupled to the voltage line 152 in the configuration exemplifiedin FIG. 26. The second voltage supply circuit 154 basically supplies afixed voltage to the voltage line 152 during exposure. It should benoted that the voltage supply circuit 154 may be a separate componentthat is independent from the voltage supply circuit 150, or the voltagesupply circuits 150 and 154 may each be part of a single voltage supplycircuit.

The control circuit 160, which is not depicted in FIG. 26, for example,determines whether or not the illuminance on the photoelectricconverters 10 is greater than or equal to a predetermined illuminance,on the basis of the level of the output signals detected by thedetection circuit 130A, before the start of a frame in which an image isto be acquired. In a case where, for example, the illuminance on thephotoelectric converters 10 is less than the predetermined illuminance,the control circuit 160, for example, drives the voltage supply circuit150 in such a way that the relatively high second voltage V2 from amongthe first voltage V1 and the second voltage V2 is applied as the resetvoltage V_(RST) to the reset voltage line 36. Each pixel Px resets thephotoelectric converter 10 on the basis of the second voltage V2, inother words, resets the potentials of the pixel electrode 12 and theimpurity region 111 serving as a charge accumulation unit.

Here, the voltage supply circuit 150 supplies a voltage of 6 V, forexample, as the second voltage V2 to the reset voltage line 36.Consequently, the potential of the pixel electrode 12 of each pixel Pxafter execution of the reset is 6 V. At such time, the voltage supplycircuit 154 applies a voltage of 12 V, for example, to the oppositeelectrode 11 of each pixel Px via the voltage line 152. In other words,the potential difference ΔV between the opposite electrode 11 and thepixel electrode 12 at such time is 6 V.

However, in a case where the illuminance on the photoelectric converters10 is greater than or equal to the predetermined illuminance, that is,in an environment having a high illuminance, the relatively low firstvoltage V1 is supplied to the reset voltage line 36 from the voltagesupply circuit 150. For example, in a case where a voltage of 1 V, forexample, is used as the first voltage V1, the potential difference ΔVbetween the opposite electrode 11 and the pixel electrode 12 increasesto 11 V compared to a state in which the second voltage V2 is applied tothe reset voltage line 36. In other words, photographing at a highersensitivity becomes possible. In this example, a voltage in the firstvoltage range is used as the first voltage V1 and a voltage in thesecond voltage range is used as the second voltage V2. Voltages in thesecond voltage range may be used for both the first voltage V1 and thesecond voltage V2. However, it is not essential to use voltages in thesecond voltage range as the first voltage V1 and the second voltage V2.

Here, an example has been described in which the second voltage V2 isapplied to the reset voltage line 36 in a case where the illuminance onthe photoelectric converters 10 is less than the predeterminedilluminance, and the relatively low first voltage V1 is applied to thereset voltage line 36 in a case where the illuminance is greater than orequal to the predetermined illuminance. However, it should be noted thatthe relationship of the applied voltage to the illuminance is notrestricted to this example. The voltage supply circuit 150 may be drivenin such a way that the first voltage V1 is applied to the reset voltageline 36 in a case where the illuminance on the photoelectric converters10 is less than the predetermined illuminance, and the relatively highsecond voltage V2 is applied to the reset voltage line 36 in a casewhere the illuminance is greater than or equal to the predeterminedilluminance. At such time, a voltage that is lower than the firstvoltage V1 may be supplied to the opposite electrode 11.

Second Embodiment

FIG. 27 schematically depicts an exemplary configuration of a camerasystem according to a second embodiment of the present disclosure. Acamera system 200D depicted in FIG. 27 schematically includes an imagingdevice 100D and a voltage supply circuit 150D.

Compared to the imaging device 100A depicted in FIG. 1, the imagingdevice 100D depicted in FIG. 27 has a common point in including theplurality of pixels Px each having the photoelectric converter 10 andthe output circuit 20, and the detection circuit 130A coupled to theoutput circuit 20 of each pixel Px. In the configuration exemplified inFIG. 27, the output circuits 20 and the detection circuit 130A are bothformed on the semiconductor substrate 110. The photoelectric converters10, the output circuits 20, and the detection circuit 130A may beprovided in the form of a package in which these are integrated.

In the configuration exemplified in 27, the voltage supply circuit 150Dis arranged within the camera system 200D in the form of a chip or apackage, for example, as an element that is separate from a package thatincludes the photoelectric converters 10, the output circuits 20, andthe detection circuit 130A, for example. For example, the voltage supplycircuit 150D may be formed on a substrate that is different from thesemiconductor substrate 110 on which the pixels Px are arranged.However, the voltage supply circuit 150D being coupled to one of theopposite electrode 11 and the pixel electrode 12 of each pixel Px issimilar to the first embodiment.

The operation in the camera system 200D may be similar to the firstembodiment. For example, the detection circuit 130A detects the level ofa signal that is output from the output circuit 20 of each pixel Px. Thevoltage supply circuit 150D applies the first voltage V1 to the voltageline 152 in a case where the level of the output signals detected by thedetection circuit 130A is lower than a predetermined voltage level, onthe basis of a drive signal from the control circuit 160. In a casewhere the level of the output signals detected by the detection circuit130A is greater than or equal to the predetermined voltage level, thesecond voltage V2 that is higher than the first voltage V1 is applied tothe voltage line 152.

In this way, it is not essential for all of the semiconductor substrate110 on which the plurality of pixels Px are formed, the row scanningcircuit 120, the detection circuit 130A, the voltage supply circuit150D, and the control circuit 160 to be integrated in the form of a chipor a package, for example. Some of these elements may be arranged inanother package or substrate, and functions similar to those of theimaging device according to the first embodiment can be demonstratedalso according to this kind of camera system configuration.

FIG. 28 schematically depicts another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. The main difference between the camera system 200D depictedin FIG. 27 and a camera system 200E depicted in FIG. 28 is that thecamera system 200E has an imaging device 100E instead of the imagingdevice 100D. Compared to the imaging device 100D, the imaging device100E has the detection circuit 130B instead of the detection circuit130A, and, in this example, the output of the detection circuit 130B isinput to the image processing circuit 164.

In the configuration exemplified in FIG. 28, the image processingcircuit 164 receives an output signal of the detection circuit 130B, andexecutes a comparison with a predetermined threshold value on the basisof the output signal from the detection circuit 130B. In other words,the image processing circuit 164 compares the input from the detectioncircuit 1306 and a threshold value stored in the memory 162, forexample, and thereby determines whether or not the quantity of lightincident on the photoelectric converters 10 is greater than or equal toa predetermined quantity of light. Data indicating the determinationresult is passed to the voltage supply circuit 150D, for example.

In a case where it has been determined that the level of the signal thatis output from the output circuit 20 of each pixel Px is lower than thepredetermined level, in other words, that the quantity of light incidenton the photoelectric converters 10 is lower than the predeterminedquantity of light, the voltage supply circuit 150D supplies therelatively low first voltage V1 to the voltage line 152. In a case whereit has been determined that the quantity of light incident on thephotoelectric converters 10 is greater than or equal to thepredetermined quantity of light, the voltage supply circuit 150Dsupplies the second voltage V2 to the voltage line 152.

According to a configuration such as that exemplified in FIG. 28, thevoltage supply circuit 150D and the image processing circuit 164 arearranged within the camera system 200E in the form of elements that areseparate from the imaging device 100E, for example, as separate chips orseparate packages, and therefore the degree of freedom of the design forthe voltage level used and/or the voltage input timing is improved andmore flexible control becomes possible. Consequently, an advantage canbe obtained in that it is possible to avoid the use of a higher voltageor an increase in the chip size.

FIG. 29 schematically depicts yet another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. A camera system 200F depicted in FIG. 29 schematicallyincludes an imaging device 100F and a light quantity detector 130F.

The imaging device 100F has a common point with the imaging device 100Adepicted in FIG. 1 in including the plurality of pixels Px each havingthe photoelectric converter 10 and the output circuit 20, and thevoltage supply circuit 150 coupled to the photoelectric converter 10 ofeach pixel Px. The imaging device 100F also includes the detectioncircuit 130B coupled to the output circuits 20. The detection circuit130B has a common point with the aforementioned detection circuit 130Ain detecting the level of the signal that is output from the outputcircuit 20 of each pixel Px; however, here, the detection circuit 1306does not have the function of comparing the detected level of thesignals and a predetermined threshold value, and mainly carries outfunctions of noise-suppression signal processing, analog-digitalconversion, and the like. It should be noted that, in this example,similar to the configuration exemplified in FIG. 1, the voltage supplycircuit 150 is coupled to the voltage line 152 coupled to the oppositeelectrodes 11, and is configured in such a way that the first voltage V1or the second voltage V2 can be selectively supplied to the oppositeelectrodes 11.

The light quantity detector 130F is arranged within the camera system200F as an element that is separate from the imaging device 100Fprovided in the form of a single chip or package, for example. The lightquantity detector 130F includes in a portion thereof a photodiode PD,for example, and detects the quantity of light incident on the imagingregion formed from the plurality of pixels Px. The light quantitydetector 130F can be a publicly known illuminance sensor moduleincluding a photoelectric conversion element such as a photodiode and anilluminance sensor IC, for example.

In the configuration exemplified in FIG. 29, the control circuit 160determines whether or not the quantity of light incident on thephotoelectric converters 10 arranged in the imaging region is greaterthan or equal to a predetermined quantity of light on the basis ofoutput from the light quantity detector 130F, for example. The controlcircuit 160, in addition, similar to the first embodiment, determineswhether to cause the first voltage V1 or the second voltage V2 to besupplied to the voltage line 152 from the voltage supply circuit 150, inaccordance with the determination result as to whether or not thequantity of light incident on the photoelectric converters 10 is greaterthan or equal to the predetermined quantity of light. The voltage supplycircuit 150 applies the first voltage V1 to the voltage line 152 in acase where the quantity of light incident on the photoelectricconverters 10 is less than the predetermined quantity of light, forexample, on the basis of a drive signal from the control circuit 160. Ina case where the quantity of light incident on the photoelectricconverters 10 is greater than or equal to the predetermined quantity oflight, the second voltage V2 that is higher than the first voltage V1 isapplied to the voltage line 152.

FIG. 30 depicts a modified example of the light quantity detector.Compared to the example described with reference to FIG. 29, a camerasystem 200G depicted in FIG. 30 has a light quantity detector 130Gincluding a light quantity detection circuit 138 instead of thephotodiode PD.

In the configuration exemplified in FIG. 30, the light quantitydetection circuit 138 includes the comparator 134, which outputs acomparison result for the voltage levels of the output signal linesS_(j) with respect to the voltage level of the reference line 132. Inother words, in this example, the light quantity detection circuit 138detects the level of output signals from the output circuits 20, andcarries out a comparison with the voltage level of the reference line132. The comparison result is returned to the control circuit 160, andthe control circuit 160 determines whether or not the quantity of lightincident on the photoelectric converters 10 is greater than or equal tothe predetermined quantity of light, on the basis of the detectionresult according to the light quantity detection circuit 138.

In this way, instead of a direct measurement of the quantity of light bymeans of an illuminance sensor module or the like, information relatingto the quantity of light incident on the photoelectric converters 10 maybe obtained by way of detecting the level of the signals that are outputfrom the pixels Px. For example, some or all of the plurality of pixelsPx arranged in the imaging region may be made to function as anilluminance sensor. The acquisition of output signals from the pixels Pxby the light quantity detector 130G may be carried out using a wiredmethod or a wireless method.

FIG. 31 schematically depicts yet another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. A camera system 200H depicted in FIG. 31 schematicallyincludes an imaging device 100H including the plurality of pixels Pxeach having the photoelectric converter 10 and the output circuit 20,the voltage supply circuit 150D, and the light quantity detector 130F.

In this example, the voltage supply circuit 150D and the light quantitydetector 130F are provided outside of the imaging device 100H aselements that are separate from the imaging device 100H. Similar to theexample described with reference to FIG. 29, the control circuit 160determines whether or not the quantity of light incident on thephotoelectric converters 10 is greater than or equal to a predeterminedquantity of light, on the basis of the quantity of light detected by thelight quantity detector 130F. The control circuit 160 causes either ofthe first voltage V1 and the second voltage V2 to be applied to thevoltage line 152 from the voltage supply circuit 150D, in accordancewith the determination result.

The light quantity detector 130G depicted in FIG. 30 may be appliedinstead of the light quantity detector 130F. In other words, the levelof the signal that is output from the output circuit 20 of each pixel Pxmay be obtained, and which of the first voltage V1 and the secondvoltage V2 is to be output from the voltage supply circuit 150D may bedetermined based on a comparison result between the level of the signalsfrom the output circuits 20 and the predetermined threshold value.

Processing at Timing of Voltage Switching and Stage Thereafter

Next, a description will be given regarding correction processingcorresponding to the timing of switching the voltage applied to thevoltage line 152. As described hereinafter, a correction correspondingto the timing of switching the voltage applied to the voltage line 152may be applied to the signal level detected by the detection circuits130A and 130B. Hereinafter, a specific example of correction processingis described with the aforementioned imaging device 100A being used asan example; however, it goes without saying that it is possible forsimilar correction processing to be applied also to the imaging devices100B and 100C and the camera systems 200D to 200H.

FIG. 32 is a drawing for describing the relationship between the timingof switching between the first voltage V1 and the second voltage V2, anda change in the level of the signals acquired by the detection circuit130A, which accompanies the switching of the voltage. In FIG. 32, theuppermost timing chart depicts the rise of a pulse of a verticalsynchronization signal VD, the timing chart immediately therebelowdepicts the rise of a pulse of a horizontal synchronization signal HD,and the next timing chart depicts a change in a voltage V_(ITO) that isapplied to the opposite electrodes 11 from the voltage line 152.

In FIG. 32, in the timing chart displayed second from the top, theperiod from the rise of a certain pulse to the rise of the next pulsecorresponds to 1H, which is one horizontal scanning period. In this 1Hperiod, signals from the pixels Px belonging to a one row from among theplurality of pixels Px are read. FIG. 32 schematically represents anoperation in each row of the plurality of pixels Px by means ofrectangles that extend in the horizontal direction. The white rectanglesin FIG. 32 represent periods in which signal charges are accumulated, inother words, exposure periods. The shaded rectangles represent periodsin which the voltage levels of the output signal lines S_(j) are read bythe detection circuit 130A. For simplicity, here, it is assumed thatthere are five rows of the plurality of pixels Px, and operations fromrow 0 to row 4 are schematically depicted. In FIG. 32, R0 to R4respectively correspond to row 0 to row 4.

In FIG. 32, the bidirectional arrows in the lowermost sectionschematically depict frame periods. The timing for the start of eachframe is the timing of the rise of a pulse of the verticalsynchronization signal VD. In the example depicted in FIG. 32, thevoltage supply circuit 150 switches the voltage supplied to the oppositeelectrodes 11 from the second voltage V2 to the relatively low firstvoltage V1 at a time tc that is during the j^(th) frame period. In moredetail, in the exposure period for each row in the j^(th) frame period,the voltage applied to the voltage line 152 is switched to the firstvoltage V1.

In FIG. 32, the hatched rectangles schematically depict periods in whichthe first voltage V1 is applied to the opposite electrodes 11, within anexposure period included in the j^(th) frame period. As is apparent fromFIG. 32, when a rolling shutter is applied, if switching between thefirst voltage V1 and the second voltage V2 is executed in the exposureperiod for each row, a period in which signal charges are accumulatedwhile the first voltage V1 is applied to the opposite electrodes 11 anda period in which signal charges are accumulated while the secondvoltage V2 is applied to the opposite electrodes 11 can becomeintermixed within one frame period. In addition, the ratio between thelength of a period in which signal charges are accumulated while thefirst voltage V1 is applied to the opposite electrodes 11 and the lengthof a period in which signal charges are accumulated while the secondvoltage V2 is applied to the opposite electrodes 11 can be different foreach row of the plurality of pixels Px.

Therefore, with an operation such as that depicted in FIG. 32, anadvantage can be obtained in that there is no effect from switchingvoltages in frame periods other than the frame periods in which voltageswitching is executed. However, on the other hand, vertical shading canoccur in an image that is based on pixel signals acquired in a frameperiod in which voltage switching has been executed. In other words,variations in brightness can occur in each row. However, this kind ofvertical shading caused by voltage switching can be corrected by meansof processing such as that described hereinafter.

The level of the signal that is output from a pixel Px is generallyproportional to the product of the sensitivity in the pixel Px and thelength of the exposure period for that pixel Px. Here, the photoelectricconverter 10 in a typical embodiment of the present disclosure can havephotoelectric conversion characteristics in which the photoelectricconversion efficiency η changes due to a change in the potentialdifference ΔV between the opposite electrode 11 and the pixel electrode12, as described with reference to FIG. 4. In other words, sensitivityin the pixels Px changes according to the voltage supplied to thevoltage line 152 from the voltage supply circuit 150. Informationrelating to the way in which the photoelectric conversion efficiency ηof each pixel Px changes due to a change in the potential difference ΔVcan be acquired in advance by means of actual measurements or the like.Consequently, first, the product of the length T1 of a period in whichsignal charges are accumulated while the first voltage V1 is applied tothe opposite electrodes 11 and the sensitivity S1 of the pixels Px inthat period is calculated. Next, the product of the length T2 of aperiod in which signal charges are accumulated while the second voltageV2 is applied to the opposite electrodes 11 and the sensitivity S2 ofthe pixels Px in that period is calculated. A correction coefficientwith which (T1*S1+T2*S2), which is the sum of the aforementioned,becomes uniform for each row is then multiplied with a digital valuerepresenting the signal level, for example. It is thereby possible tocancel the effect of voltage switching on an image. In other words, itis sufficient for a larger gain to be applied as the periods depicted ashatched rectangles in FIG. 32 become longer.

Processing for this kind of correction may be executed by the imageprocessing circuit 164 or the control circuit 160, for example. Thecorrection coefficient may be determined according to the magnitude of(T1*S1+T2*S2), and may be stored in the memory 162 or the like inadvance.

FIG. 33 depicts another example of the timing of switching between thefirst voltage V1 and the second voltage V2. Rectangles to which thickdiagonal hatching has been applied in FIG. 33 represent periods for anelectronic shutter so to speak, in which the reset transistor 26 isswitched to on for charges from the node FD to be discharged. FIG. 33 isan example of a case where an electronic shutter is implemented in rowunits before the start of the accumulation of signal charges in thej^(th) frame period. In this example, as schematically depicted by thebidirectional arrow ex in FIG. 33, a period from the end of theelectronic shutter to the start of signal reading corresponds to anexposure period of the j^(th) frame period.

As depicted in FIG. 33, also in a case where switching between the firstvoltage V1 and the second voltage V2 is executed in a scanning periodfor an electronic shutter, the ratio between the length T1 of a periodin which signal charges are accumulated while the first voltage V1 isapplied to the opposite electrodes 11 and the length T2 of a period inwhich signal charges are accumulated while the second voltage V2 isapplied to the opposite electrodes 11 can be different among the rows ofthe plurality of pixels Px.

However, also in the case where this kind of operation is applied, thevalue of the photoelectric conversion efficiency η with respect to thepotential difference ΔV is already known, and the control circuit 160can acquire information relating to the timing at which switching isperformed from the second voltage V2 to the first voltage V1 and thetiming at which signals are read. Consequently, similar to the exampledescribed with reference to FIG. 32, it is possible to apply acorrection with which (T1*S1+T2*S2) becomes uniform in each row, and itis possible to avoid the generation of vertical shading in an image.

FIG. 34 depicts yet another example of the timing of switching betweenthe first voltage V1 and the second voltage V2. FIG. 34 is an operationexample in which switching between the first voltage V1 and the secondvoltage V2 is executed during a row scanning period for reading signalsin the j^(th) frame period. The row scanning period for reading signalsin the jth frame period is schematically depicted by a bidirectionalarrow rd in FIG. 34.

In FIG. 34, the hatched rectangle in R4 schematically depicts a periodin which the first voltage V1 is applied to the opposite electrodes 11,within an exposure period included in the j^(th) frame period.Furthermore, in FIG. 32, the hatched rectangles in R0 and R1schematically depict periods in which the second voltage V2 is appliedto the opposite electrodes 11, within an exposure period included in the(j+1)^(th) frame period. As is apparent with reference to FIG. 34, in acase where switching between the first voltage V1 and the second voltageV2 has been executed in a signal reading period in a certain frameperiod, sensitivity modulation brought about by the voltage switchingaffects also the accumulation of signal charges in the next frameperiod. In this case also, it is possible to avoid the generation ofvertical shading in an image by applying a correction with which(T1*S1+T2*S2) becomes uniform in each row to the j^(th) frame period andthe (j+1)^(th) frame period.

FIG. 35 is a drawing for describing the relationship between the timingof switching between the first voltage V1 and the second voltage V2 whena global shutter implemented by controlling the potential difference ΔVis applied, and a change in the level of signals acquired by thedetection circuit 130A, which accompanies the switching of the voltage.In the example depicted in FIG. 35, the second voltage V2 is selectivelyapplied to the opposite electrodes 11 in a period from after the end ofthe reading of signals relating to a (j−1)^(th) frame period to thestart of the reading of signals relating to the j^(th) frame period.Furthermore, the first voltage V1 is selectively applied to the oppositeelectrodes 11 in a period from after the end of the reading of signalsrelating to the j^(th) frame period to the start of the reading ofsignals relating to the (j+1)^(th) frame period. In addition, the firstvoltage V1 is selectively applied to the opposite electrodes 11 in aperiod from after the end of the reading of signals relating to the(j+1)^(th) frame period to the start of the reading of signals relatingto a (j+2)^(th) frame period. In other periods, the potential of theopposite electrodes 11 is made to be a positive potential in thevicinity of 0 V, in such a way that the potential difference ΔV becomessubstantially 0 V.

FIG. 35 is an operation example of when an electrical global shuttersuch as that described in the aforementioned Japanese Patent No. 6202512is applied. In FIG. 35, periods depicted by white rectangles correspondto periods for the substantial accumulation of signal charges, in otherwords, exposure periods. In this example, in the (j+1)^(th) frameperiod, although it can be said that switching from the second voltageV2 to the first voltage V1 is executed, an accumulation of signalcharges substantially does not occur in periods in which the potentialof the opposite electrodes 11 is made to be a potential in the vicinityof 0 V, and therefore there is no generation of vertical shading causedby switching the voltage applied to the opposite electrodes 11.Consequently, the aforementioned correction processing is not required.In this way, the correction processing is not required depending on theoperation mode of the imaging device. Therefore, it is not necessary forthe aforementioned correction processing to be applied in every case,and it is sufficient for the correction processing to be executed asrequired. Whether or not correction processing corresponding toswitching between the first voltage V1 and the second voltage V2 is tobe executed may be switched on the basis of the operation mode of theimaging device, a user command, or the like.

Furthermore, in a case where photographing is to be executed at a framerate that is sufficiently high, a correction with which (T1*S1+T2*S2)becomes uniform in each row can be omitted. FIG. 36 is a drawing fordescribing an example of the relationship between the timing ofswitching between the first voltage V1 and the second voltage V2, and anoutput from the imaging device 100A. In FIG. 36, the rectangles drawnbelow the chart depicting a change in the voltage V_(ITO) schematicallydepict whether image data is valid or invalid on the basis of the signallevel detected by the detection circuit 130A.

Similar to the example described with reference to FIG. 32, in theexample depicted in FIG. 36, switching between the first voltage V1 andthe second voltage V2 is executed in the exposure period of each row ofthe j^(th) frame period. Therefore, in a case where correctionprocessing is not carried out, vertical shading caused by voltageswitching can occur in an image that is based on pixel signals acquiredin the j^(th) frame period.

However, in a case where the frame rate is sufficiently high, even ifpixel signals acquired in frame periods in which there is a possibilityof the generation of vertical shading due to voltage switching, namelythe j^(th) frame period in this example, are discarded as invalid data,as schematically depicted in FIG. 36, it can be said that the effectthereof is small. In this way, in a case where the frame rate issufficiently high, pixel signals acquired in frame periods in whichthere is a possibility of the generation of vertical shading may bediscarded as invalid data, and pixel signals acquired in other frameperiods may be selectively acquired as valid data. In the presentspecification, processing in which pixel signals acquired in frameperiods that has a possibility of vertical shading are discarded asinvalid data, is referred to as mask processing. This kind of maskprocessing is effective in a case where it is difficult to ensure aregion for mounting a circuit for executing corrections with which(T1*S1+T2*S2) becomes uniform in each row.

FIG. 37 depicts an application example of mask processing in a casewhere switching between the first voltage V1 and the second voltage V2has been executed during a row scanning period for reading signals. Asdescribed with reference to FIG. 34, in a case where switching betweenthe first voltage V1 and the second voltage V2 has been executed in asignal reading period in a certain frame period, sensitivity modulationbrought about by the voltage switching affects also the accumulation ofsignal charges in the next frame period. Consequently, in a case whereswitching between the first voltage V1 and the second voltage V2 hasbeen executed during a row scanning period for reading a j^(th) signal,pixel signals acquired in the j^(th) frame period and pixel signalsacquired in the (j+1)^(th) frame period may be set as targets for themask processing as invalid data, as schematically depicted in FIG. 37.

It is sufficient for the aforementioned mask processing to be executedas required, and it is beneficial for it to be possible to switchbetween whether or not the mask processing is to be executed. The maskprocessing can be executed by a logic circuit arranged in the controlcircuit 160, for example, or the image processing circuit 164. Theselection of data may be executed by an analog-digital conversioncircuit in the detection circuit 130A.

Reflection of Detected Exposure Quantity on Potential Difference ΔV inAutomatic Exposure Setting Process

It is not necessary for the voltages that can be supplied to theopposite electrodes 11 or the pixel electrodes 12 by the aforementionedvoltage supply circuits 150, 150D, and 154 to be restricted to the twovalues of the first voltage V1 and the second voltage V2. The voltagesupply circuits 150, 150D, and 154 may be configured so as to be able toselectively apply any voltages of three or more values to the voltageline 152 in accordance with the environment in which photographing iscarried out, for example. For example, as described hereinafter, thevoltage supply circuit 150, 150D, or 154 may be configured so as toapply a voltage to the voltage line 152 with switching being performedbetween voltages of three or more values, in accordance with theexposure quantity, that is, the illuminance on the photoelectricconverters 10.

FIG. 38 is a drawing for describing an example of a processing sequencein an automatic exposure setting process, which can be applied in animaging device and a camera system according to the embodiments of thepresent disclosure. The graph depicted in FIG. 38 depicts examples ofchanges in the exposure quantity for each frame period.

The exposure quantity indicated by the vertical axis of FIG. 38 can becalculated as described hereinafter, for example. As schematicallydepicted in FIG. 39, a region including the photoelectric converters 10of the plurality of pixels Px is taken as an imaging region Rm, and anarbitrary region including the photoelectric converters 10 of one ormore pixels Px from within the imaging region Rm is taken as a detectionregion Rd. At such time, the exposure quantity indicated by the verticalaxis of FIG. 38 can be calculated by detecting, for each frame period,the level of the signals from the output circuits 20 of the pixels Pxlocated in the detection region Rd. For example, an average value forthe level of the signals from the output circuits 20 of the pixels Pxlocated in the detection region Rd can be made to correspond to theexposure quantity. Instead of detecting signal levels by means of thedetection circuit 130A or 1306, the exposure quantity for each frameperiod may be estimated by means of the light quantity detector 130F or130G.

FIG. 40 depicts an example of processing in which a voltage that isoutput from the voltage supply circuit is altered according to theexposure quantity detected. FIG. 40 depicts a graph indicating changesin exposure quantity for each frame period, and a graph indicatingchanges in the voltage V_(ITO) applied to the opposite electrodes 11from the voltage line 152, together as one drawing. The graph in theupper section of FIG. 40 is the same as the graph depicted in FIG. 38.In the example depicted in FIG. 40, in a case where an exposure quantityexceeding a predetermined threshold value Ex1 is detected in a certainframe period, the voltage that is output from the voltage supply circuit150 is switched to a higher voltage.

In the example depicted in FIG. 40, if attention is directed to thethird frame period, for example, the acquired exposure quantity exceedsthe value Ex1. Therefore, the voltage supply circuit 150 switches thevoltage supplied to the voltage line 152 to a third voltage V3 that ishigher than the first voltage V1. Consequently, in the next fourth frameperiod, signal charges are accumulated in a state in which therelatively high third voltage V3 is applied to the opposite electrodes11. In a case where the photoelectric converters 10 have photoelectricconversion characteristics such as those depicted in FIG. 4, forexample, the sensitivity of the pixels Px increases together with anincrease in the voltage applied to the photoelectric converters 10.

It should be noted that, in this example, the exposure quantity acquiredin the fourth frame period still exceeds the threshold value Ex1.Consequently, the voltage supply circuit 150 further increases thevoltage supplied to the voltage line 152, and applies a fourth voltageV4 to the photoelectric converters 10. In a case where the exposurequantity acquired in the fifth frame period still exceeds the thresholdvalue Ex1, the voltage supply circuit 150 applies an even higher fifthvoltage V5 to the voltage line 152, as depicted in FIG. 40. In thisexample, the exposure quantity acquired in the sixth frame period isless than or equal to the threshold value Ex1, and therefore, in theseventh frame period, the voltage applied to the opposite electrodes 11remains as the fifth voltage V5. The aforementioned second voltage V2can be any of the third voltage V3 to the fifth voltage V5 that arehigher than the first voltage V1.

In this way, the voltage that is output from the voltage supply circuit150 may be switched in a multistage or continuous manner in such a waythat the exposure quantity acquired in the immediately preceding frameperiod is reflected in the photoelectric conversion efficiency in thenext frame period. In addition, in a case where an exposure quantitythat is less than a predetermined threshold value Ex2 is detected in acertain frame period, processing may be executed in which the voltagethat is output from the voltage supply circuit 150 is switched to alower voltage.

FIG. 41 depicts another example of processing in which the voltage thatis output from the voltage supply circuit is altered according to theexposure quantity detected. Similar to FIG. 40, FIG. 41 also depicts agraph indicating changes in exposure quantity for each frame period, anda graph indicating changes in the voltage V_(ITO) applied to theopposite electrodes 11 from the voltage line 152, together as onedrawing.

In the example depicted in FIG. 41, in a case where an exposure quantitythat is less than the predetermined threshold value Ex2 is detected in acertain frame period, the voltage that is output from the voltage supplycircuit 150 is switched to a lower voltage. In the example depicted inFIG. 41, the exposure quantity acquired in the third frame period, forexample, is less than the value Ex2. Therefore, the voltage supplycircuit 150 causes the voltage supplied to the voltage line 152 todecrease from the fifth voltage V5 to the fourth voltage V4. Theexposure quantity acquired in the fourth frame period is also less thanthe threshold value Ex2, and therefore the voltage supply circuit 150changes the voltage supplied to the voltage line 152 to the lower thirdvoltage V3. In a case where the exposure quantity acquired in the fifthframe period is also less than the threshold value Ex2, the voltagesupply circuit 150 applies the even lower first voltage V1 to thevoltage line 152. In this example, the exposure quantity acquired in thesixth frame period is between the threshold value Ex2 and the thresholdvalue Ex1, and therefore, in the seventh frame period, the first voltageV1 is applied to the opposite electrodes 11.

In this way, the separate threshold value Ex2 may be provided serving asa determination basis for switching the voltage that is output from thevoltage supply circuit 150 to a lower voltage. The threshold value Ex2may be less than or equal to the threshold value Ex1. In the examplesdepicted in FIGS. 38 to 41, the voltage applied to the oppositeelectrodes 11 or the pixel electrodes 12 in the next frame period isdetermined according to a comparison result between an exposure quantityacquired in the immediately preceding frame period and a thresholdvalue; however, it should be noted that the voltage applied to theopposite electrodes 11 or the pixel electrodes 12 may be determinedbased on two or more comparison results.

FIG. 42 depicts yet another example of processing in which the voltagethat is output from the voltage supply circuit is altered according tothe exposure quantity detected. In FIG. 42, in a case where the exposurequantity acquired in the immediately preceding frame period exceeds thethreshold value Ex1 twice continuously, the voltage that is output fromthe voltage supply circuit 150 is switched to a higher voltage.

If attention is directed to the third frame period, for example, theacquired exposure quantity exceeds the threshold value Ex1. At thispoint in time, the voltage that is output from the voltage supplycircuit 150 is not switched. In this example, the exposure quantityacquired in the fourth frame period does not exceed the threshold valueEx1. Therefore, the voltage that is output from the voltage supplycircuit 150 is kept at the first voltage V1.

The exposure quantity next exceeds the threshold value Ex1 in theseventh frame period. At this point in time also, the voltage that isoutput from the voltage supply circuit 150 is not switched. In thisexample, the exposure quantities acquired in the consecutive eighth totenth frame periods all exceed the threshold value Ex1. Consequently,the voltage that is output from the voltage supply circuit 150 issequentially increased after acquisition of the exposure quantity in theeighth frame period, after acquisition of the exposure quantity in theninth frame period, and after acquisition of the exposure quantity inthe tenth frame period.

In this way, in a case where the exposure quantity acquired in theimmediately preceding frame period exceeds the threshold value or isless than the threshold value continuously a plurality of times, thevoltage that is output from the voltage supply circuit 150 may beswitched to a higher voltage or a lower voltage. According to this kindof processing, for example, when a camera stroboscope is lit, whenphotographing is carried out with a light source that periodicallyrepeats flickering, or the like, it is possible to reduce thepossibility of an overflow of signal charges occurring, whilesuppressing power consumption.

Correction of Linearity Corresponding to Voltage Applied toPhotoelectric Converters 10

FIG. 43 schematically depicts an example of a change in the output ofthe detection circuit 130A with respect to an increase in the exposurequantity. In FIG. 43, a solid line L1 indicates an exemplary change inthe output of the detection circuit 130A with respect to an increase inthe exposure period, in other words, an increase in the exposurequantity, at a fixed illuminance, which is obtained in a case where avoltage in the second voltage range is applied to the oppositeelectrodes 11. A dashed line L2 indicates a change in the outputobtained in a case where a lower voltage within the second voltage rangeis applied to the opposite electrodes 11. It should be noted that, inFIG. 43, a dashed line L3 indicates an exemplary change in the output ofthe detection circuit 130A with respect to an increase in the exposurequantity, which is obtained in a case where a voltage in the firstvoltage range is applied to the opposite electrodes 11.

As described with reference to FIG. 12, a change in the photoelectricconversion efficiency η in the photoelectric conversion layer 13 withrespect to a change in the potential difference ΔV applied between theopposite electrode 11 and the pixel electrode 12 is sometimes notlinear. Therefore, according to the magnitude of the voltage applied tothe opposite electrodes 11 or the pixel electrodes 12, the output of thedetection circuit 130A may not increase proportionally with respect toan increase in the exposure period. A tendency such as this is likely toappear particularly if the potential difference ΔV is small. In theexample depicted in FIG. 43, the solid line L1 corresponds to a casewhere the voltage applied to the opposite electrodes 11 or the pixelelectrodes 12 is comparatively large, and the solid line L1 is linear.The dashed lines L2 and L3 correspond to a case where the voltageapplied to the opposite electrodes 11 or the pixel electrodes 12 isrelatively small, and the deviation of the dashed lines L2 and L3 from astraight line increases as the exposure quantity increases.

Thus, a deviation from a straight line of the output of the detectioncircuit 130A with respect to an increase in the exposure period may becorrected by correcting the output from the detection circuit 130A, forexample. FIG. 44 schematically depicts an overview of linearitycompensation processing. For example, a table for converting the outputfrom the detection circuit 130A into an appropriate digital value may beprepared for each voltage value that could be output from the voltagesupply circuit 150.

In this example, three correction tables 1 to 3 corresponding tovoltages that could be output from the voltage supply circuit 150 areretained in the memory 162. For example, the control circuit 160receives an output after analog-digital conversion or the like from thedetection circuit 130A, and applies a correction table in accordancewith the specific value of the voltage applied to the photoelectricconverters 10 from the voltage supply circuit 150. A selector 165 inFIG. 44 is a circuit that selects which of the correction tables 1 to 3is to be applied, or whether a correction table is not to be applied, inaccordance with the value of the voltage supplied to the photoelectricconverters 10 from the voltage supply circuit 150. The output aftercorrection is passed to the image processing circuit 164, and gammaprocessing is carried out, for example.

FIG. 45 depicts an example of a correction table. In the correctiontable depicted in FIG. 45, digital values after linearity compensationare given for each digital value that is an output from the detectioncircuit 130A. For example, when N is input as sensor output from thedetection circuit 130A, the control circuit 160 outputs X to the imageprocessing circuit 164. It should be noted that, in a case where avoltage that does not require linearity compensation is selected as avoltage to be applied to the photoelectric converters 10 from thevoltage supply circuit 150, as with line L1 in FIG. 43, the sensoroutput from the detection circuit 130A is passed to the image processingcircuit 164 without being altered.

By applying this kind of linearity compensation processing, as depictedin FIG. 43, the characteristics indicated by line L2 can be corrected asindicated by the solid straight line A2 in FIG. 43, and thecharacteristics indicated by the graph L3 can be corrected as indicatedby the solid straight line A3. The linearity compensation processing maybe executed by the image processing circuit 164. Instead of preparing atable for pre-gamma correction output, gamma correction may be executedusing a y value that takes deviation from a straight line intoconsideration. Alternatively, instead of converting a digital valueusing a table, linearity may be compensated by multiplying sensor outputfrom the detection circuit 130A by an appropriate coefficient.

It should be noted that deviation in linearity such as theaforementioned can be different according to the imaging device oraccording to the camera system. FIG. 46 is a drawing for describingdifferences in deviation in linearity according to the imaging device oraccording to the camera system. In FIG. 46, a dashed line M1 indicatesan exemplary change in the output of the detection circuit 130A withrespect to an increase in the exposure quantity in relation to a certainimaging device, and a dashed line M2 indicates an exemplary change inthe output of the detection circuit 130A with respect to an increase inthe exposure quantity in relation to another imaging device. It isbeneficial if the output of the detection circuit 130A with respect toan increase in the exposure quantity matches between these imagingdevices as indicated by a straight line M12 in FIG. 46, for example.

FIG. 47 schematically depicts an overview of linearity compensationprocessing in which differences according to the imaging device oraccording to the camera system are canceled. For example, in a casewhere there is an imaging device of sample 1 and an imaging device ofsample 2, data relating to photoelectric conversion characteristics suchas those depicted in FIG. 4 is acquired in advance for samples 1 and 2using testers or the like. In addition, corrected values for each sampleare calculated based on the acquired data, and the corrected values arestored in the memory 162 in the form of a table, for example. FIG. 47depicts an overview of linearity compensation processing in sample 1,for example. Correction tables 11 to 13 for converting the output fromthe detection circuit 130A into an appropriate digital value are writtenfor each voltage value that could be output from the voltage supplycircuit 150, in the memory 162 of the imaging device of sample 1. Itshould be noted that the memory 162 is typically a nonvolatile memory.

FIG. 48 depicts an example of a correction table stored in the memory162 of the imaging device of sample 1, and FIG. 49 depicts an example ofa correction table stored in the memory 162 of the imaging device ofsample 2. In a case where this kind of correction table is applied, withrespect to sensor output N from the detection circuit 130A for example,a digital value X is output from the control circuit 160 of the imagingdevice of sample 1, whereas a digital value Y is output from the controlcircuit 160 of the imaging device of sample 2. By applying this kind oflinearity compensation processing that is adapted according to theimaging device or according to the camera system, as depicted in theexample of FIG. 46, it is possible to cancel the effect of differencesin photoelectric conversion characteristics caused by individualdifferences according to the imaging device or according to the camerasystem.

As mentioned above, corrected values that are calculated based on datarelating to photoelectric conversion characteristics can be prepared foreach voltage value that could be output from the voltage supply circuit150. However, there may also be cases where exposure is carried out withthe presumed exposure time being exceeded, or where a voltage that hadnot been presumed is included in the voltages that are output from thevoltage supply circuit 150, for example.

FIG. 50 depicts another example of a correction table stored in thememory 162, and FIG. 51 depicts the plotting of output values given inthe correction table of FIG. 50. In FIG. 51, the white circles indicateplots relating to corrected values that are applied when a voltage Va isapplied to the photoelectric converters 10 from the voltage supplycircuit 150, and the white triangles indicate plots relating tocorrected values that are applied when a voltage Vb is applied to thephotoelectric converters 10 from the voltage supply circuit 150.Furthermore, the white rectangles indicate plots relating to correctedvalues that are applied when a voltage Vc is applied to thephotoelectric converters 10 from the voltage supply circuit 150.

In a case where, for example, the value of P13 has not been obtained inadvance in the correction table of FIG. 50, the value of P13 can becomputed by means of linear interpolation from corrected value P11 andcorrected value P12, for example. Furthermore, in a case where, forexample, a voltage that had not been presumed is applied to the voltageline 152 from the voltage supply circuit 150, it is possible to computea straight line indicating the characteristics of the output of thedetection circuit 130A with respect to an increase in the exposurequantity, from a discrete value given in the correction table. Asexemplified in FIG. 51, if a parameter representing a straight line Ptis calculated, for example, it is possible for a corrected value forwhen an exposure quantity between t2 and t3 a and a voltage between Vband Vc are applied to the photoelectric converters 10 to be calculatedafterward and applied in linearity compensation.

FIG. 52 schematically depicts an overview of linearity compensationprocessing including interpolation processing. As exemplified in FIG.52, the control circuit 160 can include in a portion thereof aninterpolation processing circuit 166 that executes this kind of linearinterpolation.

The embodiments of the present disclosure can be applied tophotodetectors, image sensors, and the like, and an imaging device or acamera system of the present disclosure can be used in digital stillcameras such as digital single-lens reflex cameras and digitalmirrorless single-lens cameras, or digital video cameras, for example.Alternatively, an imaging device or a camera system of the presentdisclosure can be used in various camera systems or sensor systemsincluding commercial cameras for broadcasting uses, medical cameras,surveillance cameras, or the like. It is also possible to acquire imagesusing infrared rays by appropriately selecting the material of thephotoelectric conversion layer. An imaging device that performs imagingusing infrared rays can be used in security cameras, cameras that areused mounted on vehicles, or the like. Vehicle-mounted cameras can beused as input for a control device, for the safe travel of a vehicle,for example. Alternatively, vehicle-mounted cameras can be used tosupport an operator, for the safe travel of a vehicle.

What is claimed is:
 1. An imaging device comprising: a photoelectricconverter that includes a first electrode, a second electrode, and aphotoelectric conversion layer located between the first electrode andthe second electrode; a voltage supply circuit; an output circuit thatis coupled to the second electrode, the output circuit being configuredto output a signal that corresponds to a potential of the secondelectrode; and a detection circuit that is configured to detect a levelof the signal from the output circuit, wherein the photoelectricconverter has photoelectric conversion characteristics in which a firstrate of change is greater than a second rate of change, the first rateof change being a rate of change of a photoelectric conversionefficiency of the photoelectric converter with respect to a bias voltageapplied between the first electrode and the second electrode when thebias voltage is in a first voltage range, the second rate being a rateof change of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage when the biasvoltage is in a second voltage range that is greater than the firstvoltage range, and the voltage supply circuit: supplies a voltage to oneof the first electrode and the second electrode to cause a potentialdifference between the first electrode and the second electrode to be afirst potential difference, in a case where the level detected by thedetection circuit is less than a first threshold value; and supplies avoltage to the one of the first electrode and the second electrode tocause the potential difference between the first electrode and thesecond electrode to be a second potential difference that is greaterthan the first potential difference, in a case where the level detectedby the detection circuit is greater than or equal to a second thresholdvalue that is greater than or equal to the first threshold value.
 2. Theimaging device according to claim 1, wherein the voltage supply circuit:supplies a first voltage to the one of the first electrode and thesecond electrode, in a case where the level detected by the detectioncircuit is less than the first threshold value; and, supplies a secondvoltage that is greater than the first voltage to the one of the firstelectrode and the second electrode, in a case where the level detectedby the detection circuit is greater than or equal to the secondthreshold value.
 3. The imaging device according to claim 2, wherein theoutput circuit includes: a first transistor that has a gate coupled tothe second electrode, the first transistor being configured to receive athird voltage to one of a source and a drain; and a second transistorthat has a gate coupled to the second electrode, the second transistorbeing configured to receive a fourth voltage that is greater than thethird voltage to one of a source and a drain.
 4. The imaging deviceaccording to claim 2, wherein the output circuit includes: a capacitor;and a switching element that is coupled between the second electrode andthe capacitor, and, the switching element is set to on-state when thesignal that corresponds to the potential of the second electrode isread, in a case where the level detected by the detection circuit isgreater than or equal to the second threshold value, the potential ofthe second electrode having been changed by photoelectric conversion inthe photoelectric converter.
 5. The imaging device according to claim 2,wherein the output circuit includes a capacitor that has one electrodecoupled to the second electrode, and, a potential of another electrodeof the capacitor is temporarily decreased when the signal thatcorresponds to the potential of the second electrode is read, in a casewhere the level detected by the detection circuit is greater than orequal to the second threshold value, the potential of the secondelectrode having been changed by photoelectric conversion in thephotoelectric converter.
 6. The imaging device according to claim 2,wherein the output circuit includes: a first transistor that has a gatecoupled to the second electrode; and an attenuator that is coupledbetween the second electrode and the gate of the first transistor, and,the attenuator attenuates a voltage applied to the gate of the firsttransistor, in a case where the level detected by the detection circuitis greater than or equal to the second threshold value.
 7. The imagingdevice according to claim 2, wherein a potential of the first electrodeis greater than the potential of the second electrode, in both of astate in which the first voltage is supplied to the one of the firstelectrode and the second electrode, and a state in which the secondvoltage is supplied to the one of the first electrode and the secondelectrode.
 8. The imaging device according to claim 2, wherein, in agraph of the photoelectric conversion efficiency of the photoelectricconverter with respect to the bias voltage, when Vt is a value of thebias voltage corresponding to an intersecting point between a firsttangent at a point where the photoelectric conversion efficiency risesfrom 0 and a second tangent at a point where the bias voltage is alargest value during operation, the first voltage range is a voltagerange that is less than the Vt.
 9. The imaging device according to claim2, wherein, in a graph of the photoelectric conversion efficiency of thephotoelectric converter with respect to the bias voltage, when Vt is avalue of the bias voltage corresponding to an intersecting point betweena first tangent at a point where a value of the photoelectric conversionefficiency is 0.06 and a second tangent at a point where the biasvoltage is a largest value during operation, the first voltage range isa voltage range that is less than the Vt.
 10. The imaging deviceaccording to claim 2, wherein the second voltage range is a voltagerange in which a change in the photoelectric conversion efficiency withrespect to a change of 1 V in the bias voltage is less than 10%.
 11. Theimaging device according to claim 2, wherein the second voltage range isa voltage range in which the photoelectric conversion efficiency is 0.7or more.
 12. The imaging device according to claim 8, wherein a firstefficiency that is the photoelectric conversion efficiency of thephotoelectric converter when the first voltage is supplied is less thana second efficiency that is the photoelectric conversion efficiency ofthe photoelectric converter when the second voltage is supplied.
 13. Theimaging device according to claim 12, wherein the first voltage and thesecond voltage are voltages within the second voltage range.
 14. Theimaging device according to claim 13, wherein a ratio of the secondefficiency with respect to the first efficiency is greater than 1 and1.25 or less.
 15. A camera system comprising: an imaging device thatincludes: a photoelectric converter that includes a first electrode, asecond electrode, and a photoelectric conversion layer located betweenthe first electrode and the second electrode; a voltage supply circuit;and an output circuit that is coupled to the second electrode, theoutput circuit being configured to output a signal that corresponds to apotential of the second electrode; and a light quantity detector thatdetects a quantity of light incident on the photoelectric converter,wherein the photoelectric converter has photoelectric conversioncharacteristics in which a first rate of change is greater than a secondrate of change, the first rate of change being a rate of change of aphotoelectric conversion efficiency of the photoelectric converter withrespect to a bias voltage applied between the first electrode and thesecond electrode when the bias voltage is in a first voltage range, thesecond rate being a rate of change of the photoelectric conversionefficiency of the photoelectric converter with respect to the biasvoltage when the bias voltage is in a second voltage range that isgreater than the first voltage range, and the voltage supply circuit:supplies a voltage to one of the first electrode and the secondelectrode to cause a potential difference between the first electrodeand the second electrode to be a first potential difference, in a casewhere the quantity of light detected by the light quantity detector isless than a first quantity of light; and, supplies a voltage to the oneof the first electrode and the second electrode to cause the potentialdifference between the first electrode and the second electrode to be asecond potential difference that is greater than the first potentialdifference, in a case where the quantity of light detected by the lightquantity detector is greater than or equal to a second quantity of lightthat is greater than or equal to the first quantity of light.
 16. Adriving method of an imaging device that includes a photoelectricconverter that includes a first electrode, a second electrode, and aphotoelectric conversion layer located between the first electrode andthe second electrode, the driving method comprising: supplying a voltageto one of the first electrode and the second electrode to cause apotential difference between the first electrode and the secondelectrode to be a first potential difference, in a case where a quantityof light incident on the photoelectric converter is less than a firstquantity of light; and supplying a voltage to the one of the firstelectrode and the second electrode to cause the potential differencebetween the first electrode and the second electrode to be a secondpotential difference that is greater than the first potentialdifference, in a case where the quantity of light incident on thephotoelectric converter is greater than or equal to a second quantity oflight that is greater than or equal to the first quantity of light.